I bought Dead Rising 2 a few weeks ago, and only learned that I can play TIR last week. I was having so much fun and wanted to try co-op in the game to finish off my achievements when, a few days ago, I couldn't. Every time I try, I get a message that said I do not have the correct permission to. Does this mean that the co-op and TIR is for Xbox gold members only now? Or was it a fluke that I got to play before I was found out?
99% of multiplayer games require gold membership on xbox. This hasn't changed since xbox came out. My guess is maybe you had a trial membership originally and you didn't realize it and just yes when going through the options.
That said if you even play it 2x a week online it is worth it. There are very few games that have only a single player component these days.