Most likly the broblem is too many moving things in your level. Ever notice on some games that when you have alot of activity (alot of things moving around at once) on the screen that the game slows down? Well that could be the problem. The psp is trying to load up your level but it cant handle prossesing that much information at once so it freezes and shuts down. Its like a failsafe so your psp doesnt burn itself out.
I had the same problem on my psp 2000 after I tried playing a level sombody made.