I just have this game, yesterday I can download DLC, but today I cannot download everything :(( , it just said server problem, I go to GOG website and it said 403 error, and I try to delete everything and reinstall GOG Galaxy and it still not work. Anyone help me? :((
P/s: sorry for my bad English :(

You could try to download the game without using GOG Galaxy.

Open your browser (e.g. Firefox, IE,...).
Go to the gog website.
Login to your account.
Click on Account button (in the upper right side of the website).
Now you have a list of all your games from gog. Click on Witcher 2.
Change OS and language if needed.
Download all 13 parts of the game by clicking on it and save on your hard drive. You can find them under the headline "Game Downloads".
After that double click the exe-file to install the game.
Feel free to download the game goodies.
If you wish yu can import the game later to Galaxy.

Hope this helps.

P.S. Are you sure you talk bout the Witcher 2 and not 3 because you wrote something about DLCs?

Are you able to play the game now?

Everything alright now, Thanks man :)

Nice. Have fun with your game!