friends i am able to acess ECP and all the other pages but when i am going to public folder to change the permissions and while clicking the link i am getting Unexpected error 500... not sure what is wrong as i am not able to understand the logs form eventviewer... below is the log from eventviewer..

Current user: 'domain.local/Users/Administrator'
Request for URL 'https://fighter.domain.local:444/ecp/PublicFolders/PublicFolderPermissions.aspx?pwmcid=1&ReturnObjectType=1&dtm=Isolation&id=000000003A48960742BDB94A825E87D58A255A5901004AE73BC7CCD08A44BC7D96B5C0820FE40000000000110000(https://mail.domain.com/ecp/PublicFolders/PublicFolderPermissions.aspx?pwmcid=1&ReturnObjectType=1&dtm=Isolation&id=000000003A48960742BDB94A825E87D58A255A5901004AE73BC7CCD08A44BC7D96B5C0820FE40000000000110000)' failed with the following error:
System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Exchange.Management.ControlPanel.IdentityExtensions.ToIdentity(ADObject entry)
   at Microsoft.Exchange.Management.ControlPanel.PublicFolderPermissionInfo..ctor(MailboxFolderPermission permissionEntry)
   at Microsoft.Exchange.Management.DDIService.PublicFolderPermissionService.GetPublicFolderClientPermissionEntryPostAction(DataRow inputRow, DataTable dataTable, DataObjectStore store)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.DDIService.Activity.DoPostRun(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind)
   at Microsoft.Exchange.Management.DDIService.Sequence.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.Workflow.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.WSSingleObjectDataHandler.ExecuteCore(Workflow workflow)
   at Microsoft.Exchange.Management.DDIService.WSDataHandler.Execute()
   at Microsoft.Exchange.Management.DDIService.DDIServiceHelper.Get(String workflow, Identity identity)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.ControlPanel.WebServiceReference.GetObject(Identity identity)
   at Microsoft.Exchange.Management.ControlPanel.PropertyPageSheet.OnPreRender(EventArgs e)
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   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)
   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)

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Exchange.Management.ControlPanel.IdentityExtensions.ToIdentity(ADObject entry)
   at Microsoft.Exchange.Management.ControlPanel.PublicFolderPermissionInfo..ctor(MailboxFolderPermission permissionEntry)
   at Microsoft.Exchange.Management.DDIService.PublicFolderPermissionService.GetPublicFolderClientPermissionEntryPostAction(DataRow inputRow, DataTable dataTable, DataObjectStore store)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.DDIService.Activity.DoPostRun(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind)
   at Microsoft.Exchange.Management.DDIService.Sequence.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.Workflow.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.WSSingleObjectDataHandler.ExecuteCore(Workflow workflow)
   at Microsoft.Exchange.Management.DDIService.WSDataHandler.Execute()
   at Microsoft.Exchange.Management.DDIService.DDIServiceHelper.Get(String workflow, Identity identity)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.ControlPanel.WebServiceReference.GetObject(Identity identity)
   at Microsoft.Exchange.Management.ControlPanel.PropertyPageSheet.OnPreRender(EventArgs e)
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.ControlPanel.WebServiceReference.GetObject(Identity identity)
   at Microsoft.Exchange.Management.ControlPanel.PropertyPageSheet.OnPreRender(EventArgs e)
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Exchange.Management.ControlPanel.IdentityExtensions.ToIdentity(ADObject entry)
   at Microsoft.Exchange.Management.ControlPanel.PublicFolderPermissionInfo..ctor(MailboxFolderPermission permissionEntry)
   at Microsoft.Exchange.Management.DDIService.PublicFolderPermissionService.GetPublicFolderClientPermissionEntryPostAction(DataRow inputRow, DataTable dataTable, DataObjectStore store)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.DDIService.Activity.DoPostRun(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind)
   at Microsoft.Exchange.Management.DDIService.Sequence.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.Workflow.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.WSSingleObjectDataHandler.ExecuteCore(Workflow workflow)
   at Microsoft.Exchange.Management.DDIService.WSDataHandler.Execute()
   at Microsoft.Exchange.Management.DDIService.DDIServiceHelper.Get(String workflow, Identity identity)
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Microsoft.Exchange.Management.DDIService.Activity.DoPostRun(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind)
   at Microsoft.Exchange.Management.DDIService.Sequence.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.Workflow.Run(DataRow input, DataTable dataTable, DataObjectStore store, Type codeBehind, UpdateTableDelegate updateTableDelegate)
   at Microsoft.Exchange.Management.DDIService.WSSingleObjectDataHandler.ExecuteCore(Workflow workflow)
   at Microsoft.Exchange.Management.DDIService.WSDataHandler.Execute()
   at Microsoft.Exchange.Management.DDIService.DDIServiceHelper.Get(String workflow, Identity identity)

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Exchange.Management.ControlPanel.IdentityExtensions.ToIdentity(ADObject entry)
   at Microsoft.Exchange.Management.ControlPanel.PublicFolderPermissionInfo..ctor(MailboxFolderPermission permissionEntry)
   at Microsoft.Exchange.Management.DDIService.PublicFolderPermissionService.GetPublicFolderClientPermissionEntryPostAction(DataRow inputRow, DataTable dataTable, DataObjectStore store)
   at Microsoft.Exchange.Management.ControlPanel.IdentityExtensions.ToIdentity(ADObject entry)
   at Microsoft.Exchange.Management.ControlPanel.PublicFolderPermissionInfo..ctor(MailboxFolderPermission permissionEntry)
   at Microsoft.Exchange.Management.DDIService.PublicFolderPermissionService.GetPublicFolderClientPermissionEntryPostAction(DataRow inputRow, DataTable dataTable, DataObjectStore store)