samba - Apr 2012 - Samba 3 Windows 7 Temporary Profile on 2nd Login

Hi,

I'm bashing my head against a brick wall against a strange Win7 domain 
login issue.

We have a Samba 3 CentOS server which for some months has been a problem 
free PDC for a network of about 15 Win7Pro64 clients in a school.

Recently, for some reason, the following situation has now arisen:
* After client PC reboot, domain login is fine.
* After logging out of windows, any attempt to log in again immediately 
leads to a temporary profile being loaded.
* If the client PC is left unused for several minutes, or is rebooted, 
logging in normally is possible again.

I've tried quite a number of things, including rolling back a client PC 
to an image from well before the problem occurred and removing the 
antivirus from a client PC, and nothing seems to make any difference.

If I set "Do not log users on with temporary profiles" on a client PC 
via gpedit.msc, I get an error "The user profile service failed the 
login. User profile cannot be loaded" if I try to re-log-on too soon, 
and this seems to reset the timer on when login will be possible again 
to requiring a further 2 or 3 minute delay.

After a couple of days of googling and testing, this is sending me a bit 
crazy. Has anyone else encountered a similar situation and solved or 
worked around it? Or does anyone have any insight into possible causes?

Many thanks,
Ben Clayton
Irax Ltd.