I just clicked on the downloadable content button and a prompt came up asking for this. What is it? I preordered through GoG and don't recall ever getting a code or anything.

u dont need it..just download it..

If you download patches 1.1 and 1.2, all of the preorder DLC is included. No need to download from there :)

In fact, patch 1.2 gets rid of the button altogether. It was causing problems for too many people, so they've been including DLC in the patches, instead.