Mine is not working either. Also, when you try to buy Rtts points and things like that, it says those items are not available. So I guess when the store updates it will all work. Kinda sucks.. I wanted to play online.
I had my copy since yesterday around lunchtime; but the consensus is correct ... until Sony updates their store to include BOTH the actual game and the paid version of the Online Pass, we won't be able to use the codes we have. As far as I can tell (from searching Sony sites, blogs, etc.), and from previous game purchases, the store update starts around noon PST. With the three-hour time difference here in NY (EST) we are looking at approx 3PM to update the store. Either way, I'm liking this version of MLB; the graphics, audio, controls, almost everything on the Vita version is really good so far.