Was it only on one map? Sometimes when I download a new map my game will crash when I go to start playing. If it happens two or three times, I normally delete the map file and then reconnect to the server and download it again. I'm not sure how to access the map file for a Mac. For my Dell laptop, I go to Program Files, then Activision folder, then Call of Duty 4 folder, and then finally the usermaps folder which contains all of your map files that are in individual folders. Once you're there, then click on the folder of the map that is giving you trouble and delete it. Then launch your game and download the map again upon connecting to the server. I hope this helps! Good luck!