We have users in a separate forest,  configured with a two-way trust.  I noticed that when I try to apply permissions to Global security groups in that domain,  I get an error message saying that the user does not exist or is not unique. Giving permissions to users directly doesn't give me this error. 

As far as I know,  if we have a two-way trust between domains,  there shouldn't be anything else I need to configure.  Any ideas? 

The ULS logs are below:

Name=Request (POST:http://site:80/sites/topsite/thissite/_layouts/15/aclinv.aspx?GroupId=1130&IsDlg=1)
Non-OAuth request. IsAuthenticated=True, UserIdentityName=0#.w|domain\user, ClaimsCount=122
Site=/sites/topsite
UserAgent not available, file operations may not be optimized.    at Microsoft.SharePoint.SPFileStreamManager.CreateCobaltStreamContainer(SPFileStreamStore spfs, ILockBytes ilb, Boolean copyOnFirstWrite, Boolean disposeIlb)     at Microsoft.SharePoint.SPFileStreamManager.SetInputLockBytes(SPFileInfo& fileInfo, SqlSession session, PrefetchResult prefetchResult)     at Microsoft.SharePoint.CoordinatedStreamBuffer.SPCoordinatedStreamBufferFactory.CreateFromDocumentRowset(Guid databaseId, SqlSession session, SPFileStreamManager spfstm, Object[] metadataRow, SPRowset contentRowset, SPDocumentBindRequest& dbreq, SPDocumentBindResults& dbres)     at Microsoft.SharePoint.SPSqlClient.GetDocumentContentRow(Int32 rowOrd, Object ospFileStmMgr, SPDocumentBindRequest& dbreq, SPDocumentBindResults& dbres)     at Microsoft.SharePoint.Library.SPRequestInternalClass.GetFileAndMetaInfo(String bstrUrl, Byte bPageView, Byte bPageMode, Byte bGetBuildDependencySet, String bstrCurrentFolderUrl, Int32 iRequestVersion, Byte bMainFileRequest, Boolean& pbCanCustomizePages, Boolean& pbCanPersonalizeWebParts, Boolean& pbCanAddDeleteWebParts, Boolean& pbGhostedDocument, Boolean& pbDefaultToPersonal, Boolean& pbIsWebWelcomePage, String& pbstrSiteRoot, Guid& pgSiteId, UInt32& pdwVersion, String& pbstrTimeLastModified, String& pbstrContent, UInt32& pdwPartCount, Object& pvarMetaData, Object& pvarMultipleMeetingDoclibRootFolders, String& pbstrRedirectUrl, Boolean& pbObjectIsList, Guid& pgListId, UInt32& pdwItemId, Int64& pllListFlags, Boolean& pbAccessDenied, Guid& pgDocid, Byte& piLevel, UInt64& ppermMask, Object& pvarBuildDependencySet, UInt32& pdwNumBuildDependencies, Object& pvarBuildDependencies, String& pbstrFolderUrl, String& pbstrContentTypeOrder, Guid& pgDocScopeId)     at Microsoft.SharePoint.Library.SPRequestInternalClass.GetFileAndMetaInfo(String bstrUrl, Byte bPageView, Byte bPageMode, Byte bGetBuildDependencySet, String bstrCurrentFolderUrl, Int32 iRequestVersion, Byte bMainFileRequest, Boolean& pbCanCustomizePages, Boolean& pbCanPersonalizeWebParts, Boolean& pbCanAddDeleteWebParts, Boolean& pbGhostedDocument, Boolean& pbDefaultToPersonal, Boolean& pbIsWebWelcomePage, String& pbstrSiteRoot, Guid& pgSiteId, UInt32& pdwVersion, String& pbstrTimeLastModified, String& pbstrContent, UInt32& pdwPartCount, Object& pvarMetaData, Object& pvarMultipleMeetingDoclibRootFolders, String& pbstrRedirectUrl, Boolean& pbObjectIsList, Guid& pgListId, UInt32& pdwItemId, Int64& pllListFlags, Boolean& pbAccessDenied, Guid& pgDocid, Byte& piLevel, UInt64& ppermMask, Object& pvarBuildDependencySet, UInt32& pdwNumBuildDependencies, Object& pvarBuildDependencies, String& pbstrFolderUrl, String& pbstrContentTypeOrder, Guid& pgDocScopeId)     at Microsoft.SharePoint.Library.SPRequest.GetFileAndMetaInfo(String bstrUrl, Byte bPageView, Byte bPageMode, Byte bGetBuildDependencySet, String bstrCurrentFolderUrl, Int32 iRequestVersion, Byte bMainFileRequest, Boolean& pbCanCustomizePages, Boolean& pbCanPersonalizeWebParts, Boolean& pbCanAddDeleteWebParts, Boolean& pbGhostedDocument, Boolean& pbDefaultToPersonal, Boolean& pbIsWebWelcomePage, String& pbstrSiteRoot, Guid& pgSiteId, UInt32& pdwVersion, String& pbstrTimeLastModified, String& pbstrContent, UInt32& pdwPartCount, Object& pvarMetaData, Object& pvarMultipleMeetingDoclibRootFolders, String& pbstrRedirectUrl, Boolean& pbObjectIsList, Guid& pgListId, UInt32& pdwItemId, Int64& pllListFlags, Boolean& pbAccessDenied, Guid& pgDocid, Byte& piLevel, UInt64& ppermMask, Object& pvarBuildDependencySet, UInt32& pdwNumBuildDependencies, Object& pvarBuildDependencies, String& pbstrFolderUrl, String& pbstrContentTypeOrder, Guid& pgDocScopeId)     at Microsoft.SharePoint.SPWeb.GetWebPartPageContent(Uri pageUrl, Int32 pageVersion, PageView requestedView, HttpContext context, Boolean forRender, Boolean includeHidden, Boolean mainFileRequest, Boolean fetchDependencyInformation, Boolean& ghostedPage, String& siteRoot, Guid& siteId, Int64& bytes, Guid& docId, UInt32& docVersion, String& timeLastModified, Byte& level, Object& buildDependencySetData, UInt32& dependencyCount, Object& buildDependencies, SPWebPartCollectionInitialState& initialState, Object& oMultipleMeetingDoclibRootFolders, String& redirectUrl, Boolean& ObjectIsList, Guid& listId)     at Microsoft.SharePoint.ApplicationRuntime.SPRequestModuleData.FetchWebPartPageInformationForInit(HttpContext context, SPWeb spweb, Boolean mainFileRequest, String path, Boolean impersonate, Boolean& isAppWeb, Boolean& fGhostedPage, Guid& docId, UInt32& docVersion, String& timeLastModified, SPFileLevel& spLevel, String& masterPageUrl, String& customMasterPageUrl, String& webUrl, String& siteUrl, Guid& siteId, Object& buildDependencySetData, SPWebPartCollectionInitialState& initialState, String& siteRoot, String& redirectUrl, Object& oMultipleMeetingDoclibRootFolders, Boolean& objectIsList, Guid& listId, Int64& bytes)     at Microsoft.SharePoint.ApplicationRuntime.SPRequestModuleData.GetWebPartPageData(HttpContext context, String path, Boolean throwIfFileNotFound)     at Microsoft.SharePoint.ApplicationRuntime.SPVirtualPathProvider.GetCacheKey(String virtualPath)     at System.Web.Compilation.BuildManager.GetVPathBuildResultFromCacheInternal(VirtualPath virtualPath, Boolean ensureIsUpToDate)     at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)     at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)     at System.Web.Compilation.BuildManager.GetVPathBuildResult(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean ensureIsUpToDate)     at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection)     at System.Web.UI.Page.ApplyMasterPage()     at System.Web.UI.Page.PerformPreInit()     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest()     at System.Web.UI.Page.ProcessRequest(HttpContext context)     at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()     at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)     at System.Web.HttpApplication.PipelineStepManager.ResumeSteps(Exception error)     at System.Web.HttpApplication.BeginProcessRequestNotification(HttpContext context, AsyncCallback cb)     at System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus)     at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)
Spent 0 ms to bind 30197 byte file stream
[Forced due to logging gap, cached @ 09/15/2015 09:26:05.49, Original Level: Verbose] TenantAppEtag record requested but there is no sitesubscription or tenantId for site {0} so we will use the WebApp Id for the cache.
[Forced due to logging gap, Original Level: Verbose] Local farm does not have a 'SPO-GuestSharingUIEnabled' property.  Therefore, guest sharing UI is disabled on the farm.
[Forced due to logging gap, cached @ 09/15/2015 09:26:05.59, Original Level: Verbose] Menu::OnLoad() - Was called. ID="{0}"
[Forced due to logging gap, Original Level: VerboseEx] Reverting to process identity
[Forced due to logging gap, cached @ 09/15/2015 09:26:05.68, Original Level: Verbose] SearchFromGC name = {0}. start
[Forced due to logging gap, Original Level: Verbose] SearchFromGC name = {0}. returned. Result count = {1}
The user does not exist or is not unique.
SPRequest.UpdateMembers: UserPrincipalName=i:0).w|s-1-5-21-1469851039-782320854-270368766-46787, AppPrincipalName= ,bstrUrl=http://site:80/sites/topsite/thissite/ ,dwObjectType=0 ,bstrObjId= ,lGroupID=1190 ,lGroupOwnerId=1 ,bRemoveFromCurrentScopeOnly=False ,bSendEmail=True
System.Runtime.InteropServices.COMException: The user does not exist or is not unique., StackTrace:    at Microsoft.SharePoint.SPUserCollection.UpdateMembers(Object objUpdateInfo, Object objAddIds, Object objRemoveLogins, Object objRemoveIds, Boolean fSendEmail)     at Microsoft.SharePoint.SPUserCollection.AddCollection(SPUserInfo[] addUsersInfo, IEnumerable`1 addUsers)     at Microsoft.SharePoint.ApplicationPages.AclInv.<>c__DisplayClass12.<PrepareStrategyForGroupSharing>b__11()     at Microsoft.SharePoint.ApplicationPages.SharingStrategy.Share()     at Microsoft.SharePoint.ApplicationPages.AclInv.HandleInternalUsersOrGroups(SharingStrategy strategy, List`1 userInfoList, List`1 userList, List`1 groupList, SPUserCollection resolvedUsers, Boolean sendWelcomeEmailChecked, Boolean includeAnonymousLink)     at Microsoft.SharePoint.ApplicationPages.AclInv.BtnOK_Click(Object sender, EventArgs e)     at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument)     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest()     at System.Web.UI.Page.ProcessRequest(HttpContext context)     at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()     at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)     at System.Web.HttpApplication.PipelineStepManager.ResumeSteps(Exception error)     at System.Web.HttpApplication.BeginProcessRequestNotification(HttpContext context, AsyncCallback cb)     at System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus)     at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)
Application error when access /_layouts/15/aclinv.aspx, Error=The user does not exist or is not unique.   at Microsoft.SharePoint.Library.SPRequestInternalClass.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)     at Microsoft.SharePoint.Library.SPRequest.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)
System.Runtime.InteropServices.COMException: The user does not exist or is not unique.    at Microsoft.SharePoint.Library.SPRequestInternalClass.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)     at Microsoft.SharePoint.Library.SPRequest.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)
Getting Error Message for Exception System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> Microsoft.SharePoint.SPException: The user does not exist or is not unique. ---> System.Runtime.InteropServices.COMException: The user does not exist or is not unique.     at Microsoft.SharePoint.Library.SPRequestInternalClass.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)     at Microsoft.SharePoint.Library.SPRequest.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)     --- End of inner exception stack trace ---     at Microsoft.SharePoint.SPGlobal.HandleComException(COMException comEx)     at Microsoft.SharePoint.Library.SPRequest.UpdateMembers(String bstrUrl, UInt32 dwObjectType, String bstrObjId, Guid& pguidScopeId, Int32 lGroupID, Int32 lGroupOwnerId, Object& pvarArrayAdd, Object& pvarArrayAddIds, Object& pvarArrayLoginsRemove, Object& pvarArrayIdsRemove, Boolean bRemoveFromCurrentScopeOnly, Boolean bSendEmail)     at Microsoft.SharePoint.SPUserCollection.UpdateMembers(Object objUpdateInfo, Object objAddIds, Object objRemoveLogins, Object objRemoveIds, Boolean fSendEmail)     at Microsoft.SharePoint.SPUserCollection.AddCollection(SPUserInfo[] addUsersInfo, IEnumerable`1 addUsers)     at Microsoft.SharePoint.ApplicationPages.AclInv.<>c__DisplayClass12.<PrepareStrategyForGroupSharing>b__11()     at Microsoft.SharePoint.ApplicationPages.SharingStrategy.Share()     at Microsoft.SharePoint.ApplicationPages.AclInv.HandleInternalUsersOrGroups(SharingStrategy strategy, List`1 userInfoList, List`1 userList, List`1 groupList, SPUserCollection resolvedUsers, Boolean sendWelcomeEmailChecked, Boolean includeAnonymousLink)     at Microsoft.SharePoint.ApplicationPages.AclInv.BtnOK_Click(Object sender, EventArgs e)     at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument)     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.HandleError(Exception e)     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)     at System.Web.UI.Page.ProcessRequest()     at System.Web.UI.Page.ProcessRequest(HttpContext context)     at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()     at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Micro Trace Tags: 0 nasq,4 agb9s,31 ak8dj,210 aix9j,0 ai1wu,0 8nca,0 tkau,30 ajlz0,1 aat87
Leaving Monitored Scope (Request (POST:http://site:80/sites/topsite/thissite/_layouts/15/aclinv.aspx?GroupId=1190&IsDlg=1)). Execution Time=292.9624

If security groups belongs to different forest, you should use universal groups instead of global groups. You can create a universal group and nest the required global groups inside it as members. You can then assign permissions to universal groups as they are replicated across all GCs.

Hope this helps.