Give this commandline a try, I helped some people with the same problem and it workedPaste the file in the game directory and try to launch SP.http://www.mediafire.com/file/1fusqfq6namff6n/commandline.txt/file
Try installing the game into another directory maybe? Change the compability of the EFLC.exe(orwhateveritis), run it as administrator, open singleplayer, play a bit, save after the first mission, try joining IVMP again.
I think I remember when my IVMP didn't launch the game, then I decided to play singleplayer, saved and tried again and it logged in. I'm guessing it's because it needs to load the textures and stuff and singleplayer does this to prepare the textures for multiplayer?
I don't really know if it's commandline related, but give it a tryGive this commandline a try, I helped some people with the same problem and it workedPaste the file in the game directory and try to launch SP.http://www.mediafire.com/file/1fusqfq6namff6n/commandline.txt/file