Once you’ve set Steam not to run in compatibility mode, run Warzone 2.0 again and check if the problem has been resolved. Disable compatibility mode for Modern Warfare 2 / Warzone 2.0: ...

Are you getting an annoying "compatibility mode" message every time you run iTunes in Windows 7? A quick trip to the Registry should get rid of it.

Select the Compatibility tab. Select the Run This Program in Compatibility Mode option. From the drop-down list, choose the operating system you ran before upgrading to Vista.

For Windows 7 users requiring access to older apps, it's a fine guided tour of a feature that doesn't just jump out at users and explain itself.