Alteriwnet Error

Hey guys, I get this problem that my iw4mp.dat doesnt work when i start alteriwnet.. ive played the game for several months with the same file but suddenly it just stopped working. could somebody please help me out? i really want to play mw2 again :S
tried to unpack the files over and over again but same problem

THANKS FOR ALL REPLIES! SOLVED NOW THANKS

Delete your cache.xml and enable updates..

has there been an update than? :O