Explorer.exe not loading on XP systems

I recently ran into a problem where intermittently the explorer.exe process was not running when XP users logged on. The result was a blue background with no icons displayed - if you ran ctrl alt del and started a new process, explorer.exe the desktop loaded fine and all was well.

There was lots of chatter about spyware and hijacked browsers, but that was not the issue. I was trying to determine if SP3 or perhaps the Symantec EndPoint virus software was the culprit as both were installed about the same time.

As it turns out, Symantec posted a comment about this on their support site in respect to login scripts. If you create a new GPO like this:

Computer Configuration, Administrative Templates, System/Scripts
Policy Setting - Run logon scripts synchronously

This allows the login script to load, antivirus to scan, and the explorer.exe process to execute!