Guest Account Logs on then loggs off immediately

Can anyone help? This is driving me crazy.

My Guest account briefly shows "Welcome" When logging on then logs off again
immediately.

There are no errors in the event log, just a successful logon (event 4624),
followed one second later by a user-initated logoff (event 4647).

I have tried turning the account off and on. Turning it off then completely
deleting the guest folder in "users" and completely removing all references
to the guest account "-501" in the registry. Still the same behaviour. The
Guest account folder is successfully recreated as are the registry entries,
but the account still logs on then off on its own.

I have seen the knowledgebase entry:

http://support.microsoft.com/kb/929825

But I do not see the error mentioned in my event log, I have checked the
registry key mentioned and it is fine. All accounts but the guest account
work fine.

Any ideas?!

Thanks.

 

I have discovered that using netplwiz to change the guest user to the
standard users group allows it to work. However, as soon as I turn it back to
being a member of the guests group the old behaviour returns.

Any clues?

Thanks.