Forum:Undead Nightmare Offline

It's been about a year since I last played this game... Now I cannot get the DLC to load. It says I need to be connected to the internet to play...

Single Player > Undead Nightmare > "ALERT: Unable to connect to the network. Please check your connections and try again"

I have done some looking around, and could not find anything about needing to be online just for single player. Do I just need to live without? I have the downloaded version, if that counts for anything.