Hey.

I wanted to create a back-up for my Witcher 2 but gog keeps saying that it looks like the code isn't from gog I even used the specific link for the Witcher.. The code works, because I just activated my install with it. Can someone point me in the right direction? While it's not super urgent, it's always nice to have a back up in case I lose my boxed game.

Where (which URL) are you using the code?

That "doesn't look like one of our codes" is the message that you get when you try to redeem a free game with a wrong code:
https://www.gog.com/redeem
GOG gift/free game codes consist of a sequence of 20 numbers and letters, numbers ranging from 0 to 9 and letters from A to F.

But I think in order to get the backup from your physical copy you need to introduce your game key here:
https://www.gog.com/witcher/backup
(I don't have a physical copy so I can't confirm). You know what the CD key looks like. ;)

I hope this helps. Otherwise, don't hesitate to contact the very friendly and helpful GOG Support.