COD - Modern warfare 2 error while playing

Solution

I had the same problem and found the solution on de disc itself by activision support.

Zone file errors are most likely due to a bad install or corrupt game files.

You can verify the integrity of the game files in the Steam client.
In the Steam client

• Right-click on the game and select properties.
• Click on the local files tab and click the "Verify integrity of game cache" button.
• You will need to do this for the single player and multiplayer game executables.