when i went to play a co-op vs. ai game on my level one account, it continued to search for a game, and at 15 minutes, i tried to exit the queue, and the client responded with "You cannot leave the queue now as a match has been made and Champion Selection is imminent!"

It is still searching for a queue to join.
EDIT:relogged and it occured again

I too have been encountering the same issue. The same message also appears if you try and exit the client and so far the only way that I have found to exit is by manually closing the client through the Windows Task Manger.

http://na.leagueoflegends.com/board/....php?t=2198429

This is the longest thread we have so far; maybe a red will see it.