I understand. And it seems to drag out doing it via message board as I would have tried all of these things in a 10 minute time frame. I'm afraid without seeing your setup I am not sure what else to look for. It generally just works for me, and especially on 10.6 server.
So could you type or post a screenshot of the exact message you are seeing when the user launches Pro Tools, just to make sure we are on the same page?
Here are the next things I would do if I was on the problem:
Copy permssions down in the Applications folder on the workstation. Attempt log in.
Install Pro Tools on another workstation.
Allow access to all members of the group and see if other users on a different workstation have rights to run the software.
Try not managing Applications at all, allowing users of the workgroup to have access to all applications.