For some reason which is beyond me, whenever I try to join a multiplayer MW3 game through the lobby, it comes up with message "No servers found" in the search dialog on the top right of the screen. Last night, it actually found 3 available games in TDM, I managed to join one, it was extremely laggy and unplayable.

When I try to join a dedicated server, it comes up with a message in the middle of the screen saying "Server is a different version 1.4". I can not join onto friends, or have them join my lobby. I am still able to host a private game, and play in it etc, but no one can join me.

I have tried defragmenting the cache files, verifying the cache files, turning off firewalls, a full virus scan, reinstalling Steam, and a system restore to 5 days prior, and still the problem persists.

The most recent software change I done prior to this happening, was installing GameBooster. It worked well when I first used it, no problems at all. Then I went back on after a few hours of having my computer turned off, and that's when I first noticed the issue.

Since all the fixes I have done are mostly local, I would assume that the problem is with Steam or something else that isn't my computer.

I did send them a support ticket, but Steam never really has been reliable.

Checked your router for port forwarding etc?

Actually it sounds like your game is not up to date.. Say you have game client 1.3, and servers are up to 1.4, you're not going to find anything.

Maybe look down that avenue?

I use a mobile modem (Those stupid little usb things that gives you internet on-the-go!) so there aren't many things I can alter.

Also I checked the version and it says in-game that my version is 1.4.386somethinsomethin, and Steam doesn't want to update anything.

1.4.386 is the latest update, I saw a thread like this. Trying to remember will get back to you when I do.

Wow, It just went away. Everything works now, thanks a lot for the help guys.

+1 for you.