File's different from the server

when i go with my friends it sais sometimes "File's different from the server"any ideas?

Verify integrity of game cache in Steam

didnt work -_-

ok since the DLC was released many players are having this problem even me what i think is happening is i have the DLC so say im hosting and some1 joins who has not got the DLC that person would have different files than the host so would be kicked same applys the otherway around if host dont have the DLC and you do then you still get kicked trust me this is doing my nut in, nothing can be dont about it until them make a fix i have tried removing all the DLC file i thought it worked until i got to the third match and was kicked i think i got lucky with the first two games lol there is even a thread on the steam forum and i think iW have tweeted about it so it says on the steam forum i dont know i dont use twitter lol

Then you guys just have to wait for a new patch

identical problem! my mw3 is original!!

my friend bought the dlc too and had the same problem.
i told him to verify the steam cache and it worked without any problems