iPad에서 이전보기로 돌아 가면 iPhone에서 완벽하게 작동하는 동안 응용 프로그램이 종료됩니다

내비게이션 바를 표시하기 위해 여러 가지 방법을 시도했지만 작동하지 않습니다. 그래서 secondViewController에 뒤로 버튼을 넣었고 iPhone에서는 완벽하게 작동하지만 iPad에서는 앱을 종료합니다.

 - (IBAction)back:(id)sender {

        [self.view endEditing:YES];
        if ([[UIDevice currentDevice]userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {

            LuanchViewController* SVC = [[LuanchViewController alloc] initWithNibName:@"LuanchViewController_iPhone" bundle:nil];
            [self presentViewController:SVC animated:YES completion:nil];
        }
        if ([[UIDevice currentDevice]userInterfaceIdiom] == UIUserInterfaceIdiomPad) {
            [self.view endEditing:YES];

            LuanchViewController* SVC = [[LuanchViewController alloc] initWithNibName:@"LuanchViewController_iPhone" bundle:nil];
            [self presentViewController:SVC animated:YES completion:nil];
        }

        [self dismissModalViewControllerAnimated:YES];
        }

오류 :-

2013-10-16 18:44:42.775 iOS-test-harness[7095:c07] -[ViewController back:]: unrecognized selector sent to instance 0xa2accb0
2013-10-16 18:44:50.193 iOS-test-harness[7095:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController back:]: unrecognized selector sent to instance 0xa2accb0'
*** First throw call stack:
(0x2c18012 0x1e8ce7e 0x2ca34bd 0x2c07bbc 0x2c0794e 0x1ea0705 0xdd42c0 0xdd4258 0xe95021 0xe9557f 0xe946e8 0xe03cef 0xe03f02 0xde1d4a 0xdd3698 0x2e51df9 0x2e51ad0 0x2b8dbf5 0x2b8d962 0x2bbebb6 0x2bbdf44 0x2bbde1b 0x2e507e3 0x2e50668 0xdd0ffc 0x240d 0x2335)
libc++abi.dylib: terminate called throwing an exception