This seems to be happening to a lot of people. One of the players on our server has this exact same error. The PC in question used to be mine and I can log into the server with my account from it. We ran the launcher and had it clear old data. Deleted the Fun Pimps and 7d2d folders from within the 'AppData' folder in user folder. Also deleted the 7d2d folder from within the SteamAppsCommon folder.
Clean install from Steam, same problem recurs.
Has anyone had a successful resolution to this issue?