The only reason I suggest work-arounds is that I host a dedi for MW4: Mercenaries and anything I can do to prevent crashing and freezing (either by accident or upset players) is a good thing... =)
Anyway, I assumed that all missions in Multi-Mission-Pack.vp, MV_Complete.vp, and Root_fs2.vp are problems for FSPort (is this a correct assumption???). There is nobody online to test this with, but I made a FSPort .vp that
seems to work. I threw up a dedicated server for a few minutes and joined it, there are definitely less missions to pick from...
Just put it in your FSPort directory to test it out... If it doesn't work maybe it's something that can be tweaked to work properly. Only the host needs it, not the clients.
http://bs.beckament.net/files_pub/NoFS2Missions.7zp.s. - be kind, I am the FS2 n00b... lol