I had the same issue Completely exit steam Run a search on your install directory for the 'missing' file IE: zone_invasion.ff Once you have found the file, delete it. Startup steam and goto the MY GAMES list, right click MW2 and select properties. From the properties window select local files, then click verify intergrity of game cache Steam will come back and tell you a file, file(s) are missing and will start to download a new copy of the one you deleted earlier.
Aug 29, 2015 Call of duty modern warfare 3 zone folder free download Call of Duty: Modern Warfare 3 (c) Activision 112011.RELEASE.DATE. PROTECTION.: Steam 2.