I've had this issue several times, very frustrating, makes the addon essentially useless if you can't get an invite; I've tried re-installing several times, that solved the issue once, but once I logged out I had the same issue. One time Oqueue excepted the friend request and I was able to talk to the person trying to invite me to the premade, and he couldn't even invite me via WoW's in game interface. Is there a solution?! Thanks!