When you try to log on to a Windows Vista-based computer by using an account that does not have administrative permissions, you briefly receive a “Welcome” message, and then you receive a “Logging off” message. Additionally, you may receive a warning in the Application Windows log that resembles the following:

The Windows logon process has failed to spawn a user application. Application name: . Command line parameters: c:\windows\system32\userinit.exe.

Source: Winlogon 
Event ID: 4006 
Level: Warning 

This issue does not occur if you log on to the computer by using an account that has administrative permissions.