I was so desperately hoping this would turn out to be timely advice, since my tress just decided to unlink this week (went a LOT longer this time, at least!) Unfortunately that tip isn't working for me. I'll probably let it go for another day of being logged out... just in case, but somehow I think I'm going to be stuck having to re-upload the tree and send out all the invites yet again... *sigh*.
Thanks for the tip, though! Maybe next time it will work for me. :(