2k does not allow you to make multiple connections to a shared network server from the same workstation if you attempt to use more than one set of credentials. If you attempt to make two or more connections to the same server using two or more sets of credentials, you will receive the error message you see.
A simple resolution to this problem would be to disconnect the previous connection(s) to the server.
This behavior is by design for security purposes.
If you require more info about this error, go to *support.microsoft.com/kb/106211/EN-US/
