I recently purchased a new desktop and am trying to install my purchased license for MC 12 on it. I successfully requested a temporary license replacement for my original license purchased back in June of '06, but when I go to install it, it is for MC 13 and is not valid for MC 12. It asks if I want to upgrade (for $19.98) ...
Looks like no one from JRiver is online just now, but have you inversed the version numbers or something? I don't understand how an MC12 license can state that it is valid only for MC13.
Does the email you got from the restore system state that the license is for MC12? Do you, by any chance, have an older MC11 license too?
It is now possible to by a new MC13 licence and use it with the latest MC12 builds, but certainly a license from 2006 should not be an MC13 licence and in any case an MC13 license should work with MC 12.0.531.
Something strange is going on if what you said is correct and you did not make a mistake with the version number. I hope you still have some of the trial period left so that you can continue to use MC12 until the problem is solved.
My old MC12 registration works with the latest build, though I have not restored it for ages.