Jonathan Arbib

Leopard:
sudo dscacheutil -flushcache

Tiger:
sudo lookupd -flushcache

Close all Office products running
Create a temporary folder on your desktop
Move “Microsoft User Data” folder under Documents to the temp folder
Move all com.microsoft.* under ~/Library/Preferences to the temp folder
Move Microsoft folder under ~/Library/Preferences to temp folder

Open any Office application such as Word or Excel. This should take you through the registration process once more and clear the error.