When I put the CD-Key obtained Steam tells me:

Your product key is not valid!

Make sure You have Entered the code exactly as it Appears (if you need you can try few more times). If your key does not seem to work or You have misplaced your product key, please click here to visit CD Projekt RED's product code verification page.

The WItcher 2 CD-Key works perfectly.

that I can do to make me admit the Key?

Sorry for my English XD

Yep, same here

Same, looks like an issue. Luckily I save my purchase emails and submitted via the long route.

Same here.

I'm in the same boat as well.

edit: This is the main topic probably

Same problem here.