You have not entered a valid product key or the key is incorrect

The following two errors show up for Microsoft Office 2007 and 2003 users for a couple of reasons.

Error #1
The key is incorrect. Verify that you have the correct key, and then retype it.

Error #2
You have not entered a valid Product Key. Please check the number located on the sticker on the back of the CD case or on your Certificate of Authenticity.