A friend of mine sent me a party invitation. I tried accepting it, but then I got the message that I don't use the latest version of dota (obviously my friend hasn't updated his game, because he has been playing for a long time without quitting). I've tried clicking it again, then tried declining it, but it kept showing me the same message even after restarting the game, hiding almost my whole screen. Even when he stopped playing, the window didn't get removed. I guess someone else should send me another invite to replace that one.
I hope you can do something about this, although it doesn't seem to be something that happens often.

EDIT: Oh, it disappeared..