Problem buying the BMP

I'm trying to buy the BMP from their craptacular online store and I see a big red warning:
"This item requires you have an account with at least one of the full campaigns on it."

Fine, I have all 3 of them. So I go on account details-->upgrade account. They require to insert a Guild Wars key (25 digits). I'm trying with both my Prophecies key and Nightfall key (Factions got lost somewhere), with no success.

Message for both: Invalid Serial Code.

What am I supposed to do?

Did you enter the store from the GW log-in screen?

no, It says "be sure to log off from the game before blabla"

Go to the log in screen. In the top right you'll see a big picture about the bmp and a button that says something like, click to enter store. When you do, it will ask you to sign in to your ncsoft account.

Thanks, got it.