当我使用一个单例，调用一个类型对象的时候，程序出现了崩溃

　　具体报错如下，希望可以得到解决：

2014-06-28 08:57:46.508 XYZ[707:1403] *** Assertion failure in -[UIKeyboardTaskQueue waitUntilAllTasksAreFinished], /SourceCache/UIKit_Sim/UIKit-2935.137/Keyboard/UIKeyboardTaskQueue.m:368

2014-06-28 08:57:46.509 XYZ[707:1403] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[UIKeyboardTaskQueue waitUntilAllTasksAreFinished] may only be called from the main thread.'

*** First throw call stack:

(

0   CoreFoundation                      0x0266e1e4 __exceptionPReprocess + 180

1   libobjc.A.dylib                     0x023ed8e5 objc_exception_throw + 44

2   CoreFoundation                      0x0266e048 +[NSException raise:format:arguments:] + 136

3   Foundation                          0x01fcd4de -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 116

4   UIKit                               0x01800166 -[UIKeyboardTaskQueue waitUntilAllTasksAreFinished] + 167

5   UIKit                               0x0128ff11 -[UIKeyboardImpl setDelegate:force:] + 442

6   UIKit                               0x0128fd52 -[UIKeyboardImpl setDelegate:] + 60

7   UIKit                               0x01556dc5 -[UIPeripheralHost(UIKitInternal) _reloadInputViewsForResponder:] + 956

8   UIKit                               0x01560a0e -[UIPeripheralHost(UIKitInternal) _preserveInputViewsWithId:animated:] + 550

9   UIKit                               0x011d7940 -[UIViewController presentViewController:withTransition:completion:] + 3317

10  UIKit                               0x10f9078f -[UIViewControlleraccessibility(SafeCategory) presentViewController:withTransition:completion:] + 71

11  UIKit                               0x011d8aef -[UIViewController presentViewController:animated:completion:] + 130

12  XYZ                                 0x0007e613 __33-[LoginViewController UserLogin:]_block_invoke + 483

13  Foundation                          0x02108ac5 __67+[NSURLConnection sendAsynchronousRequest:queue:completionHandler:]_block_invoke_2 + 151

14  Foundation                          0x02068d65 -[NSBlockOperation main] + 88

15  Foundation                          0x020c1c79 -[__NSOperationInternal _start:] + 671

16  Foundation                          0x0203e9c8 -[NSOperation start] + 83

17  Foundation                          0x020c3f44 __NSOQSchedule_f + 62

18  libdispatch.dylib                   0x030854d0 _dispatch_client_callout + 14

19  libdispatch.dylib                   0x03071fe0 _dispatch_async_redirect_invoke + 202

20  libdispatch.dylib                   0x030854d0 _dispatch_client_callout + 14

21  libdispatch.dylib                   0x03073eb7 _dispatch_root_queue_drain + 291

22  libdispatch.dylib                   0x03074127 _dispatch_worker_thread2 + 39

23  libsystem_pthread.dylib             0x033b4dab _pthread_wqthread + 336

24  libsystem_pthread.dylib             0x033b8cce start_wqthread + 30

)

libc++abi.dylib: terminating with uncaught exception of type NSException