I missed the new serial number on the upgrade package. It accepts this, and then checks for a previously installed version of Photoshop. It also goes through activation process ala Windows XP.
Coincidentally, SBC/Yahoo asked me to roll the system back from PM to AM of same day to clear up a browser problem. I hadn't made any system changes that day, so I was willing to do it. However, Photoshop then claimed the computer had changed and insisted on reactivation. The problem was, when it tried to reactivate, it:
1. Couldn't detect an active broadband connection.
2. Claimed the serial number, which it was displaying,
to me was 'too short'.
3. Refused to proceed without a valid serial number.
(Catch 22)
I had to call Adobe for, as I recall, an authorization code. I wish they would debug these authorization schemes before imposing them!