title: iOS Application tried to present modally an active controller
body: <p>I am trying to present a view controller modally from another view controller that is the second view inside UINavigationController. 
  But it keep giving error and crashing. Application tried to present modally an active controller</p>
  
  <p>I dont know what does it mean. Following is the way how i am calling. </p>
  
  <pre><code>UIStoryboard *storyBoard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone" bundle:nil];
      FBPreviewPostViewController *previewPostViewController = [storyBoard instantiateViewControllerWithIdentifier:@"FBPreviewPostViewController"];
      previewPostViewController.delegate = self;
      previewPostViewController.selectedImg = selectedImage;
      [self presentViewController:previewPostViewController animated:YES completion:nil];
  </code></pre>
  
  <p>Thanks</p>