Not that I can offer any specific help
, other than to suggest you lookup the old bugs in JWS with Windows (I have no bookmarks for them, but there were workarounds to try out) but it may be useful to know what webserver is providing the JNLP.
I would suggest doing a "telnet server.com 80" and
GET / HTTP/1.1
...since that will, amongst other things, give you the precise version of the webserver. This is likely to be useful info to Sun if you need to log a bug.
You could be *really* diligent and download Ethereal, and packet-sniff to see what HTTP message was being returned that killed JWS. For instance, it could be that the webserver is suffering an intermittent problem (e.g. overloaded, being hit by a port-scanner or weak DoS attack etc), causing it to return a non-standard (possibly even illegal) HTTP response to the webstart request.
Most webservers available today (like most web browsers) are broken, despite the simplicity of the HTTP protocol