I recently Purchased Microsoft Flight Simulator X Gold Edition (Which includes the game and Acceleration Expansion Pack) And I used the product key to activate the base game. That worked, and then I installed Acceleration and tried to activate it with it's product key. It said the Product Key was invalid. I contacted support over the phone, and they said play it for half an hour, and then an ID Code should come up. I did that, but it said "Unable to Retreive Code". I contacted support again, they referred me to Another department, They told me to go on the support website, and the support website asks me to select my product, and Flight Simulator X isn't on the list.

This problem may occur for one or more of the following reasons:

The product key is not entered correctly.
The CD-set number, the disc assembly number, or the part number was entered instead of the product key.

The product key for one product was entered for a different product. To troubleshoot this problem, try the following methods in the order in which they are presented from this Microsoft KB article and check if it helps:

"Product key not valid" error in Microsoft Games, MapPoint, or Streets and Trips

http://support.microsoft.com/kb/812467/en-us