User Environment Log is useful in troubleshooting login issues. UserEnvLog is not enable by default, this is how you enable it:
1. Create this folder if it does not exist: %windir%\debug\usermode
2. Create a registry subkey "Diagnostics" under HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion
3. Create a new DWORD key GPSvcDebugLevel
4. Enter the value 30002 (hex) http://blogs.technet.com/b/instan/archive/2008/04/17/troubleshooting-the-intermittent-slow-logon-or-slow-startup.aspx
5. Reboot your machine and login, you should be able to find the Gpsvc.log in the folder %windir%debug\usermode directory.
Enabling winlogon.log
1. Navigate to the this registry key.
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\GPExtensions\{827D319E-6EAC-11D2-A4EA-00C04F79F83A}.
2. Edit this value : ExtensionDebugLevel DWORD 2
3. Reboot
4. Log file will be located at %systemroot%\security\logs
