Profile loading problem

Regularly my users get a temporary profile loaded on Vista Home Premium.
Rebooting the PC always fixes the problem.
This only appears to happen when there are already other users logged on and the other users have multiple programs running. It appears to be some sort of resource issue - my PC has 4 GB of memory and heaps of disk space.

However, when I search the Web, all I find are articles claiming that the profile(s) are corrupt or deleted and providing instructions about recovering from corrupt profiles.

Clearly my profiles are not corrupt.

If you have any clue about the REAL cause of the problem, I would be keen to know.

Have all the accounts running, then switch to the one with the most resource intensive apps running and use Process Explorer to inspect what is running and how many resources are being used. Also have a look at reliability monitor.