Fresh Win 7 Upgrade UAC cannot authenticate

I keep getting variations on an error "UAC cannot authenticate user." When I try to run authentication I get the specfic code 0x8007241.

Background: I tried to used the Upgrade Assitant disk on a Dell 530s and it always failed stating that that the 530s was not upgradable to Win 7. The Windows Upgrade Analyst was OK. I ran the set from the Win 7 disk and did an in place upgrade. All the apps seem to work OK but any task that used to invoke UAC on Vista fails.

An additional problem is the the upgrade assitant keeps popping up at the first step and cannot be disuaded from appearing. It won't run probably because of UAC errors.

If I go to User Control I see my login with 'Administrator' under the name. If I click on the UAC settings it just blinks - no error but the process doesn't present anything.

I have GB of files that I don't have a good way to back up otherwise I would do a fresh install.

What are my options?