If you downloaded any product keys for Microsoft Office 2010 Professional Plus from Microsoft Developer Network (MSDN) or Microsoft TechNET, you most certainly have a problem.

Microsoft recently sent out a notice stating:

MSDN and TechNet subscribers who obtained their product keys for Microsoft® Office Professional Plus 2010 and Visio® Professional 2010 products earlier than May 1, 2010 may not see certain product features enabled. We apologize for this inconvenience.

Instructions on how to resolve this:
http://support.microsoft.com/kb/983473

Note that any product keys obtained after May 1, 2010 are the updated keys that enable full product functionality. All of the impacted keys have been removed from Subscriber Downloads, so the keys displayed alongside the product or on the My Product Keys page are the correct keys to use.
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The knowledgebase support article above details how to resolve the activation problem with certain features in this product key bungle.