Julie,
First, make sure that the TCPIP.NLM is the latest version available.
Second, check to see if maybe the error is occuring while it's
processing a large file.  If so, the server may be timing-out the
client session if it's taking too long to send the file.  You can
change a parm in your server options file (I think it's IDLETIMEOUT) to
make the client sessions not time-out too soon.