With my game, when I install it, it states that it's updated the game.
Yet there are no updates in the downloads folder, and the game is still v1.0.
The launcher and patching system are broken.
Viglione: Hmm, trying to run the 1.2 patch and it's saying the game is invalid or incomplete.
Make sure you're using the correct patch for your version.
The best way to do it is to update manually to v1.1.
Then let it auto-update, and you can grab the correct 1.2 patch from "\Documents\Witcher 2\Downloads".
Also, if you have DLC installed, that can break the patch.
Delete any DLC in "C:\Games\The Witcher 2\CookedPC" prior to installation.
EDIT: Nevermind, it appears to have sorted itself for you.