|Am I correct in believing that you have customised login screen installed and therefore have a non default wellcome screen? The title of your problem suggests that to be the case.|
The welcome screen, is what you see after your computer boots up. It lists all of the computers accounts and if they're password protected asks you for verification. This is controlled normally in the default case by a file called logonui.exe located in the C:\Windows\System32folder.
If I am right then either the file UI.exe is corrupt or you have a corruption in your registry that invokes the logonui file. You need to determine which of these is the case and correct the error.
Look in your registry at:
and check the value of UIHOST. I suspect it may read logon\ui.exe.
If it does then look in Windows/System32 and
Check that the directory logon exists
and check that the file UI.exe exists in the logon sub directory.
If the dir and file does exist then the UI.exe file may be corrupted. You could try and replace it with a backup copy or from wherever you got this new welcome screen theme from.
☺ When everything else fails, read the instructions.