This morning when I was playing on a large map and I was hosting, I lost. I left the game and when I tried to host a new game I got the message "map already in use"
I disconnected for the server, closed the game, deleted all auto saves, log in and still got the error.
Repeated the above steps (nothing to delete) rebooted my computer, reset my modem logged in and same error.

Changed map size, same error.