I am repletedly getting following error, please help

Error: is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Authentication.ActiveDirectory.ADSI.Utilities.AddADSIPath(String Path, Path ADSIPath) at DotNetNuke.Authentication.ActiveDirectory.ADSI.Utilities.GetRootEntry(Path ADSIPath) at DotNetNuke.Authentication.ActiveDirectory.ADSI.ADSIProvider.GetNetworkStatus() at DotNetNuke.Authentication.ActiveDirectory.Settings.UpdateSettings() --- End of inner exception stack trace ---

Yes, I get this error, when I update/enable the AD Authentication.

I did try the "impersonation" as covered in the Documentation, but still the same problem

Actually inspite of the error it does work, but it does not show the Logged-in Username, it displays blank, for the Logged-in username but the Login changes to Logout (meaning the Used does get logged in, but the Display name is blank ) 

it is the fresh DNN Install, infact I also tried Installing the AD provider while setting up the DNN

And it works too, the issue is, it is not guaranted to work, I reinstall the whole Installation and it works.

Further, I was wondering, will it be possible to have an addtional checkbox to import all existing AD users, When one enables the AD Authentication ?