iPhone app crashes when executing block code, without any console output

Here is my button action method on ViewController_1. After I click it, it will bring up a new custom view CHMenuView.

- (IBOutlet)centerButtonAction:(id)sender 
{   
    CHMenuView *menuView = [[CHMenuView alloc] init];

    [menuView addMenuItemWithTitle:@"take picture"
                       andIcon:[UIImage imageNamed:@"camera_ps.png"]
              andSelectedBlock:^{
                  NSLog(@"take picture");

                  // If I comment out all the rest code below in the block
                  // the app won't crash, and it will print "take picture"
                  // in the console  
                  UIImagePickerController *imagePicker =
                  [[UIImagePickerController alloc] init];

                  if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])
                  {
                      [imagePicker setSourceType:UIImagePickerControllerSourceTypeCamera];
                  }
                  else
                  {
                      [imagePicker setSourceType:UIImagePickerControllerSourceTypePhotoLibrary];
                  }
                  [imagePicker setDelegate:self];
                  [self presentViewController:imagePicker animated:YES completion:nil];
              }];
    [menuView show]; 
}    

CHMenuView is a custom view, and it has CHMenuItemButton on it. If I clicked the CHMenuItemButton, the block code defined in "andSelectedBlock" will get executed, and the app crashes.

This is the instruction pointer points to when the app crashes:

- (void)buttonTapped:(CHMenuItemButton*)btn
{
    [self dismiss:nil];
    double delayInSeconds = CHMenuViewAnimationTime  + CHMenuViewAnimationInterval * (buttons_.count + 1);
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        btn.selectedBlock(); // Thread 1: EXC_BAD_ACCESS(code=1, address=0x600)
    });
}

No console output. If I comment out all the UIImagePicker stuff in the block code, NSLog() will print the string, and app won't crash. But the block code seems harmless to me, I don't know what I had done wrong.