I too am on webtv, and every so often I get that message when clicking on things here. It isn't very often, and I don't know the reason why, but I just move to something else, and the next day it is fine. (Could be sooner, I don't know)
For a long time this would happen to me when clicking on the "Who is online" link. Now it never happens there and it now seems to happen in specific backgammon games when I'm trying to move. I have no idea if it is a webtv problem or a brainking problem.
Just wanted to let you know you arent alone. And again, it is fixed when you go back at a later time.