Win2K Licensing problems

Hi there.
The screnarion I have looks like this:
1 Win2k server (Active Directory Domain controller), also acting as a file server.
5 WinNT workstations and 3 Win2K workstations all members of this domain.
Problem:
Several times a day a messagewill pop up on workstations saing that there are no free network connections to the server left.
We reboot the server and the problem goes away for several hours, then comes back again.

We have oficial licenses for all PC’s, and I have checked the Licensing in administrative tools. The server is set in Per Server mode with 20 licenses.
Any idea what can be done to prevent the licenses being locked by PC’s and not released for others?
Thanks a lot,
Victor