7.3.5 RC registration problem

I installed the RC but it doesn't acknowledge my key when I enter it.

Any suggestions?

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Even worse, I did a system restore as re-installing 7.3 was not doing anything and left the RC, and now 7.3 is installed but it won't accept my entered key either!

Looks like I'm going to have to do a full OS restore from an image back-up, sigh ...