Getting this error when i click Edit button:

And here is the related log:

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)