Clean reinstall - original Vista system now on W7 pro - cannot activat

I originally bought a system with Vista. Then I upgraded it to W7 home premium. Then a few years later I did anytime upgrade to W7 pro. I just had to clean reinstall, but realized that my anytime upgrade key for W7 pro won't work to activate. Do I have to go all the way back to Vista (I'd really like to never have that pile of crap on my machine again) or can I just install the W7 home premium ISO from digital river and then do anytime upgrade?

Any tips on how to shortcut this process would be great. Should I just call tech support?

No, you don't need the Vista key or even to have Vista on the drive when you install Home Premium.

But you do need to install and activate the Home Premium first and then insert the Professional key into Anytime Upgrade to unlock the few extra expensive features which most consumers don't need:
Windows Anytime Upgrade - How to
Compare Windows 7 Editions

Once you get a perfect install set up and running best I'd capture a backup image this time so you never have to do all of that again, just reimage C in 20 minutes: Backup Complete Computer - Create an Image Backup
Imaging with free Macrium

A perfect install? Everything is compiled here that works the best in tens of thousands of Win7 installs we've directly helped do with since beta: Clean Reinstall - Factory OEM Windows 7

Thanks very much. Tried calling Windows support. They basically tried the fix already posted other places on here where you edit the registry to indicate that there's a prior version of windows and then log in with the upgrade key.

My concern is that if I install Home Premium, which I got as an upgrade version of Vista, I'm going to be in the same boat where the upgrade key won't work for the new installation. Do you know if that is the case? If so, it's a pretty terrible system Microsoft has created. I don't want Vista on my box ever again. It was terrible.

As long as there is any OS on the drive, the installer will see it and allow use of Upgrade version key during Clean Reinstall - Factory OEM Windows 7

If not skip Activation during install and then afterwards do the Option Two workaround in Clean Install with a Upgrade Windows 7 Version to activate Win7 on a new or wiped HD.

This worked like a charm. It activated correctly using the update product key for W7 prem. Thanks so much guys!! The tutorials are excellent and much appreciated.