i got the same thing. "code could not be found" what of B$ is this
I was having the same problem. Just got it to work. theres a fix listed in the other post that isn't quite clear. I'll tell you what I did tho.
At this point you've probably already granted permission to the contest app.
First, go thru the motions for voting till you get to the point of choosing your free content and select dlc.
Next open a new window, go to facebooks apps management and remove the contest app.
Now go back to the dlc window where you are suposed to like the page.
Be quick, like the page and make your selections but DO NOT
Open a new window and in this new window go back to the contest page and begin to vote again. You should get a popup asking you to log into the app via facebook. login and re-grant the permission then go back to the window with the confirmation promt and finally select corfirm and you should then get your code.
You might want to bookmark the contest page as it with be quicker then bring up CAG and clicking thru links till you get there. Hope this helps out.