I just realized the date of the original post and this won't help them, but if you are searching for answers as I did, maybe this will help.
I posted this in another thread, but sounds like you have the same problem I have. I can watch youtube, and even trailers, but I cannot watch any of my purchased movies and I can't rent movies either. It originally started after my 5.1 update and sporadically I would get the error in loading content...now I get an iTunes connection error as well.
So, I finally decided to pay 20 bones for support to find out what is wrong. Apple support confirmed there is a "number of people" having this issue and he thought there would be an update soon since they have been working on the problem for a couple of weeks. And he told me they wouldn't charge me for the call.
A little frustrating.
Message was edited by: kojiericson