network transfers die off

I have a 2000 Server, with default installations, SP2, and a share on it. when clients connect to it to upload, the are fine for the first few minutes, then the transfer of files stops and it says “error copying file the specified network name no longer exists”. the server is running ICS also. after this occurs, the internal interface cannot be pinged or anything.
I searched google for this error, but no luck. any ideas??

thx