FWIW I'm JB'd on 4.2.1 and watched 2 innings of the Red Sox game the other day and it played fine....so maybe you're indeed hitting a road block somewhere.
Just a question. I have an iPhone4, 4.2.1 JB with Greenpois0n. I have an MLB Premium subscription. I am logged in and I haven't been able to see any video for any Red Sox game since the beginning of ST. I am in NY. Could you tell me how you watched a Red Sox game? I must be doing something wrong.