I had this problem, it is very easy to solve: disable uac (user account control).
Go to microsoft control panel, user accounts and family safety, user account, change user account setting, then drag the bar down to "never notify", then try the dlc again
FluxMorz: What entitles you to receive these other DLC items? I pre-ordered on gog and I got all the gog extras but the only DLC I can get is the Troll Trouble quest.
And speaking of the quest. I have downloaded it fine but when I attempt to install it, it says administrator access is required (and I'm on my Win 7 admin account). Thoughts?