Are you having a problems playing DLC maps for MW3 on Xbox or PS3? Are you seeing the red text: “Playing with original maps only. Download all DLC content you are entitled to from the STORE in order to play DLC maps”
What has happened is that the newest DLC hasn’t been downloaded or downloaded properly. Here’s instructions for the Xbox, which are pretty similar to the PS3.
First thing you can try is to install the remaining DLC and then goto the Dashboard. Here’s a link with step by step instructions published by Activision: http://support.activision.com
If that doesn’t work, what you will need to do to fix the problem with only being able to play the original maps, is delete the newest set of DLC content, even if they appear to have been downloaded correctly, for example Decommision and Offshore say ‘Installed‘ but Vertigo says ‘Available to Download‘. You need to delete Decommision, Offshore and Vertigo from the HardDisk via the dashboard menu and the reinstall them in the MW3 game.