I was getting the connection error messages on the Witcher 2 launcher whenever I used it. The launcher had accepted my DLC codes as valid, but was unable to download them. I followed the instruction to delete registry keys under HKEY_CURRENT_USER\Software\CD Projekt RED\The Witcher 2\Downloads given here and as a result the launcher now connects just fine, but tells me that my codes are invalid!

Does anybody have any suggestions? I think the game itself is great, but this kind of messing about and lack of attention to detail (or actual proper game forum) just sours the whole thing for me.