I am getting a different error from PlayerToPlayer.lua, because of a different add-on. Till now, I had no problems using it (with API v*.*04 that is), on new API update they removed this event: EVENT_QUEST_SHARE_UPDATE
Now, my add-on auto-accepts shared quests if I so desire, but now sometimes the pop-up stays there even though you accepted the quest, and trying to accept a "nil" thing throws that error... I think the event that they have removed was supposed to check for that thing and remove the pop-up or something...
http://i.imgur.com/mdzPz6J.jpg
http://i.imgur.com/1MtlKMq.jpg