receiving: HTTP/1.1 304 Not Modified error trying to receive a stream

Having trouble accessing a streaming video file over a wan connection. This was working fine, but something seems to be giving me trouble. A packet trace shows me sending a request to the server:
GET /filename.asx HTTP/1.1

but then I receive an error in the reply
HTTP/1.1 304 Not Modified

and a request for
GET /filename.nsc HTTP/1.1

but then I receive an error in the reply
HTTP/1.1 304 Not Modified

Any idea what might be going on here. The workstations trying to connect are Win98 and XP
and the server streaming the info is Win2k sp2.
All machines local to the server's subnet can connect with out trouble. Their log shows:
GET /filename.asx HTTP/1.1
HTTP/1.1 200 OK

GET /filename.nsc HTTP/1.1
HTTP/1.1 200 OK