I have this same problem.
Lags like hell when I try to use multiplayer and wont load up the server list.
And single player works perfectly

@Zergzilla - Can you see the FL global list server? If you can play on your own LAN then DirectPlay works and by extension DirectX works so that's good. If so can you see ping values in the FL global list for the different servers? Anything greater than 250 msecs will be hard to play and lag you out.

For FL client you need no INCOMING ports so you need not open any ports in any firewall EXCEPT ZoneAlarm. ZA must be taught so you can open the OUTGOING ports FL client uses. Also I have read v5 and higher doesn't work at all with FL, use a lower version of ZA or turn off ZA while playing FL MP.

@Loso - Won't load up the FL global list is usually a failure of DirectX. Reinstall with the latest version, currently v9.0c.

@Both of ya - If you log into a server and then try to play but all you see is lag? It could be you have the wrong mod installed. Either no mod for a modded server or a loaded mod for a plain vanilla, unmodded server. Sometimes before the crash you'll see up to a minute of red lag. Make sure your current mod status matches the server's mod status.

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Earendil
SysAdmin of Boston Freelancer server
Server community website & forum: EarendilsPlace.net (server rules)

Could be Packetry problems. even on an ADSL connection i can completely DoS the connection if i fling maximum-size ICMP packets to a null address. check for all internet-capable programs and how much theyre being used. also run virus scans for trojans. a home internet connection can usually only handle one or two multiple outgoing traffic connections. any more than that and it slows significantly (this also goes for internet connection sharing)

I have directx 9.0c already