We just added an outside contractor as a collaborator on a number of tasks. When I sent him a link, it went to the page but then displayed a "Task or Folder not shared with you...." message. He clicks on it and it goes away, but if he goes to a subtask or another task he is assigned to it will display that error message and, once again, he can click on it and goes away. Every time he goes away and comes back the message reappears.
So an annoyance rather than a blocker, but still kind of annoying. Any solution?