Sitecore Edit User exception in User Manager

Question

I am trying to figure out what might be wrong. Basically, I am not able to edit any user accounts. Once I click Edit in User Manager I get the attached exception.

Any advise would be much appreciated.

Sitecore version is 6.6.0 (rev 130214)

here is the exception from the log file:

**6136 11:49:33 FATAL An uncaught exception occurred 
Exception: System.Web.HttpUnhandledException 
Message: Exception of type 'System.Web.HttpUnhandledException' was thrown. 
Source: System.Web 
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) 

Nested Exception 

Exception: System.NullReferenceException 
Message: Object reference not set to an instance of an object. 
Source: Sitecore.Client 
at Sitecore.Shell.Applications.Security.EditUser.EditUserPage.PlaceInFrame(String urlString) 
at Sitecore.Shell.Applications.Security.EditUser.EditUserPage.OnLoad(EventArgs e) 
at System.Web.UI.Control.LoadRecursive() 
at System.Web.UI.Control.LoadRecursive() 
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)**

Answer 1

I replaced the whole of the shell folder as suggested and the issue disappeared. I assume it was either missing or corrupt file.

Answer 2

Please try to replace your bin folder with fresh Sitecore dll's.