After many attempts and seeing the issue on the forum and facebook left unresponded or acknowleged by TTG, and attempting the Un-official fix as found on these forums with no sucess. I had uninstalled the game from my pc and went to my order history to 'start from scratch'.
After re-installing the game and attempting to 'get' episode 2, I received the connection error.
This would mean what? Makes me think that TTG has blocked season pass holders from further downloads. Clearly the cause is not in the files for episode 4 or all other downloads (which previously worked) would still be available as before.