Certain users are unable to log in using Active Directory credentials

I work for IT for a department at a university, and some of our users are unable to log in to some of our computers using their Active Directory credentials. The problems are few and far between; we have only encountered it around five times this year. Basically, the user logs in as normal, but the cursor eventually turns to the spinning wheel of death and the computer sits there. We left it for around an hour and it just sat there. An upgrade to Mountain Lion fixed the issue (they're currently on 10.7.5), so we did it on one computer, but a whole lab is affected now and we cannot upgrade all of the computers as some of the programs do not support Mountain Lion. (Normally when we have this issue, the user has it on only one computer. Several users are now having it on every computer in one of our labs; all were imaged using the same image via DeployStudio.)

There is no disk space issue, all other Active Directory users can log in just fine, and our local account can log in. The problem exists with only a few users, and we have no idea what could be causing it or how to fix it without doing an upgrade to Mountain Lion, which is unfortunately not an option for this lab.

Any help would be greatly appreciated!