This is an error that occurs from time to time (it indicates that something went wrong with the activation system during download or installation), and we're currently working with Digital River to find out why. Uninstalling and downloading again will probably resolve this problem. If it doesn't, please click Activation Support and follow the instructions to get an activation key from us.
Also, do you think you could answer a couple of questions for us so we can try to get to the bottom of this?
1) Where did you download the game from?
2) What were the steps you took between when you downloaded and when you got this error?
3) Did this problem happen with any other episodes? When did you download the other episodes?
4) What security software do you have installed?
5) Do you know of any software that's installed that might remove the /Temp or /tmp directory on your computer?
6) What operating system are you using?
7) Is this your first attempt to activate the game, or did it activate normally before and then revert to demo status?
8) Is this the same computer you downloaded onto, or did you move the setup file to another computer?
9) How do you connect to the internet?
If you don't want to post this info in the forum you can send it to me in a PM. Thanks!