So, I format my computer, re-install everything, VSE included, and then I remember I need a code. I had one, but obviously lost it, so I re-activate my email address to get my code, got the code, put it it, and voila...
The reg key you entered is invalid. Make sure you put it in right.
The code you got was only valid for the actual installation/user combination and not any other. You will need to register again. Don't worry, it is allowed and free forever.