Great for single-payer, but does MP even work?

It is nice to be able to play without putting wear and tear on my optical drive. But why does the multi-player mode say that the "CD key is in use"? Does the App Store have one CD key for everyone? Aspyr does not seem to get this. Their first response was the usual: delete preferences. And the same error occurs. I guess they really, really want you to buy the CD.....

kray2097151 about Call of Duty®