I have had this problem 5 or 6 times now, all resulting in leaves for my account...
So frustrating because not only can i not connect back to that game no matter what i do, but i can't start a new game until that one is done and i get a leave.
Please resolve this problem as fast as you can, it seems to happen once every 15ish games to me and as far as i can tell, i am doing nothing differently between the time where i join a game and it begins except for maybe alt-tabbing a few times.
Also, i had trouble selecting a hero during the most current instance, i tried picking allistar(who i have not bought yet) and even though he is still free this week, it says i cannot play him yet others could. I proceeded to pick blitzcrank and then the error occured and i couldn't reconnect.
I hope that helps in any way, Good Luck jesse