yea, i got the same problem, but mine locked up at lvl 37, i dont know y..it also locked up on single player(the normal map) once on like lvl 42...crap.
Trix to not get locked on a level: Dont get too mutch tower/power for where you are. i mean if you are too strong for the level there are trigers that lock you. i know thins because i made a maze of crap and put whosyourdaddy and all goes well.
normal map DONT say cheat if on single played. even if you finish it.