1. make sure the mod you're trying to play on your server is compatable with the MP server.
2. if you happen to have any previous saved games...chances are likely that is causeing the crash. You'll have to get rid of the previous "saved games" then try again.

Restore your backups. Close the FLMM. Go to My Documents\My Games\Freelancer\accounts\Multiplayer & Single Player and delete the mulitplayer and single player folders. (or move them somewhere else if you want to go back to them some other time)
Close: then go back and open FLMM and activate the mod (or mods) .
Open up the FLServer...make your entries...then "minimize" it.
Start Freelancer and choose Multiplayer, then LAN. Your server should show up.
If it doesn't, you might have to make an exception in your firewall settings.

I got it, but how to ensure that it works in MP??
sorry, I don't know how, becose I created it myself



Edited by - Lasho on 3/31/2007 4:17:00 PM

download flscan and scan for errors you might be puting stuff together that does not belong together.

Well, hopefully when reading the "readme" of the particular mod, it might reference whether or not it is MP compatable. I know for certain the OSP lite by Xerx, Chips & Argh is not compatable with MP and specifically states that in the readme file.
Most mods you get when you first download the FLMM are pretty much compatable with MP except the "No Story" mod. If you check the downloads section here, most of them will indicate if they are compatable or not.