For whatever it's worth, my experience is I cannot join EU games from Americas, but the EU guys can join my games in America. Seems to be a one way issue from my experience.

Last night while trading (its 8.20am here now, Australia) I had difficulties with an EU>Americas trade. The other person was from EU, and they weren't able to join my games - via friends list, or when re-logging to get on Americas. After 30 mins of trying, I had to re-log Americas and join their Americas game. So I guess this one went the other way =/ the EU person wasn't able to join me no matter what