Problem running multiple sessions.

We are running Windows Server 2000 on our network server and have client pc’s running both Windows 98 and Windows 2000 OS. Pc’s running 98 can open multiple sessions of programs on their machines but when a program is started on a 2000 machine no other sessions are aloud. We have disabled browse master on all the clints pc and have the master assigned to the server. Does anyone have any ideas as to why this is happening?