hey guys, i had the same problem, here's what i did (it worked perfect):
1. Close all Microsoft Office applications.
2. Click Start, click Run, type regedit in the Open box, and then click OK.
3. Locate the following registry subkey:
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\12.0\Registration
Delete the following entries:
• DigitalProductID
• ProductID
when you start office again, enter your product key, then click next, then
install now. it will update your key, and ask you to activate. it should work
fine. let me know if this helped