W2k server with disconnecting 95 / 98 cl

We are running a network with several 2000 servers with 95 and 98 clients. The cabling has been tested and checked. Every once in a while the mapping to a network drive is no longer active, it appears with an X if you go to “my computer”. All youneed to do to reconnect is go to “Network Neighborhood” and click on the server. You don’t have to re-map. Just opening the server, and the connection is restored….any ideas???
Thanks,