How to fix "Steam must be running to play this game" error

This quick guide will teach you how to fix the annoying "Steam must be running to play this game" error for Mw3:

1. Run steam as an administrator
2. Run Mw3
3. If you don't want to have to run steam as an sdministrator every time you want to play, right click steam.exe > properties > Compatibility > Check the box run as administrator.

Hope this helped you!
Note: I have only tested this for windows 7 because that's what I use, so this may not work for other operating systems.