Well, I bought the Map Pack 1 & 2 for MW3 and like a lot of people seem to be getting errors when trying to play them. From what I'm seeing it all comes down to issues with a recent steam update and not telling the MW3 devs about it. IMO this seems like just he said she said BS cuz no one wants to take the blame for this big booboo!!

Well to my point: have you gotten the error that will not allow you to play the new maps even though you bought/downloaded/installed them?

Here is what I found worked for me. It took a lot of taking what others did and putting it altogether and it seems to work on my end. Others may find that only part of what I list here will work and others may not find it helps at all.

Step 1: Shut down Steam (make sure it is 100% off ~ look in task manager processes as well as sometimes even if you turn it off it will stay in there active.

Step 2: Delete the "appcache" folder found here "C:\Program Files (x86)\Steam"

Step 3: Start Steam up and let it update the files.

Step 4: Go to your Steam "LIBRARY" and look for "Call of Duty: Modern Warfare 3" <-- This should be your single-player not the multiplayer.

Step 5: Right-click it and pull up the Properties as seen below.

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Step 6: A new box will appear with tabs across the top. Look for the tab called "LOCAL FILES" as seen in the image below.

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Step 7: Click the button "VERIFY INTEGRITY OF GAME CACHE..." (this may take a few minutes so don't panic.)

Step 8: Repeat steps 4 through 7, but for "Call of Duty: Modern Warfare 3 multiplayer."

Step 9: At this point I rebooted my PC but you can skip this part if you wish.

Step 10: Start up the single-player MW3 and once in change over to the multiplayer.

These steps worked for me I do hope they help some of you all out there.

Good Luck and Happy Gaming!!