I am having the same issue described at this address http://www.cocoabuilder.com/archive/cocoa/288659-iphone-nsmanagedobjectcontext-save-doesn-crash-but-breaks-on-objc-excep
First, when using multithread with CoreData I had few problems when
passing NSManagedObject around the app. Instead, as documented by
Apple, I end up passing NSManagedObjectID and reconstruct the full
object.
Second, when you don't have anything logged, it is likely related to
memory issues, try to run the profiler especially, but not only, looking for 'Zombie', it
should tell you more.
Finally, make sure you have initialized the context correctly, I had
similiar problem because the model from momd file was not found and
not loaded.