maybe this helps?
I dont know if this helps but I ran into a similar problem. I didnt look into vista carefully enough and just bought the upgrade because someone just said select clean install and everything will be ok. Well, it wasn't, after i performed the clean install, by bypassing entering the activation key even though it says you may ruin the key and have to purchase another one, i tried to activate and i got an error message saying this key cannot be used for a clean install and only for an upgrade. Solution: loaded up the vista dvd and performed an upgrade over the original vista install and it let me activate it. I'm more of a novice at this so I am not too positive of any negative consequences, such as ruining the product key for future installs, but as of right now everything seems to be working fine. I'd appreciate some feedback on this matter for future reference. Also if I'm way off base with consideration to your immediate problem..my apologies.