Connections Windows NT Server 4.0

In the past few months I have had a few problems with my NT 4.0 servers:
1. When accessing user manager for domains the following error: Insufficient system resources exist to complete the requested service. (I reboot the server and then it works)
2. Another NT 4.0 Server that 8 people access is returning the following error message: to many users on this remote computer. (It is not remote) Again, a reboot and all is fine.
Any ideas? Thanks
Cindy