CoreData EXC_BAD_ACCESS，无法在地址:0x00000000访问内存KERN_PROTECTION_FAILURE

I have a program using CoreData and a navigation controller. If I add a entity that is connected to my main entity through a relationship than back out to the table view of all entries and the back into the same, recently edited, entry my program crashes. My code is very similar, and for the CoreData part the same, to Apples sample code iPhoneCoreDataRecipes.I have a program using CoreData and a navigatio