主窗口关闭时，Cocoa应用程序似乎崩溃

My application seems to have acquired a slightly odd behaviour when it terminates. When I close a the main window using the standard little red button in the top left the application crashes. I haven't made any changes to the application that would obviously cause this problem. I'm struggling to debug the problem because the application crashes and my debugging skills are limited. Does anyone know any obvious reason why this might occur or a debugging strategy that I might be able to adopt?My application seems to have acquired a slightl