I received a crash report,but I do not know what happened with my Application?

It looks like your calling [[UIDevice currentDevice] systemVersion] from two separate threads at the same time – given that UIDevice is not declared as thread safe there is no guarantee this will work correctly in all cases, and I suspect thats what happened – the implementation (which ends up going through a couple of other libraries) doesn't work when used from multiple threads at once.

If you need this information from multiple threads at once, you should request it once at launch from the main thread and then query your own cache of it from then on.