Masteries screwed up during draft pick

During a Ranked team pick i was looking at a friends mastery page when the join game indicator popped up and i accepted. But when i did my mastery pages were replaced with his. And even the game didn't what to think. When ever i clicked on one of them the Game gave me this Message: "Error. A suitable error message could not be found" And i had no access to any of my masteries at all. Could some one please tell me why this occurred?