User can’t log in if someone has logged in before on that machine

Hey, I have intergrated with AD & everything is great, makes so much more sense as I now only have 1 set of user data to keep upto date. But since intergrating with AD I am plagued with people getting stuck at the login screen, it only happens if somone has logged in previously. If I reboot the machine it's fine, but if I log in & log out & anyone else tries to log in again the login window grey's out & hangs there. note you can log into a local account fine just not a network account. FYI: the users have 2 home directories, one for PC's which reside on a windows 2003 server & one's for the Mac's which reside on an Xraid, I don't know if this has anything to do with it. Log files show no sign of anything wrong anywhere. Any help anyone can shed on this would be great as it's annoying to continuiously tell user's to switch it off & back on (insert reference to the IT crowd tv show here) thanks in advance Dave Maltby