I recently had a problem with a 2008 VM that would run its customization every time it would boot. Doing some quick research people seemed to think it was a problem with the sysprep directories.
However this was a 2008 VM and 2k8 doesn’t use those directories on vCenter like XP/2k3/etc during customization. So the actual part of the fix that did work was to do a little registry editing. Removing the sysprepDecryptor.exe registry entry from the session manger key and rebooted.
Delete the sysprepDecryptor.exe registry entry.
Value name = BootExecute
Default Value = autocheck autochk *
So delete the portion after the * in the registry.