Microsoft posted an article about this, with reference to repair:
<a href="http://support.microsoft.com/default.aspx?scid=%2fsearch%2fviewDoc.aspx%3fdocID %3dKC.Q302740%26dialogID%3d2167290%26iterationID%3 d1%26sessionID%3danonymous%7c1916303" target="_blank">Running Repair on Windows XP Requires the User to Re-Activate the Product (Q302740)</a>

The part that will help out here the most is this:

"...back up and save the Wpa.dbl file after successful activation and then manually restore it after the repair process is finished and after you log on to the computer."

The same thing could be done in your situation, just restore the post activation version of this file to the same PC following a fresh install. It should solve all of your problems.

This topic has been discussed several times, I am surprised that no one recalls the fix...