title: Cant dismiss UIAlertView, buttons not clickable
body: <p>I have the following code where i show a MBProgress view and then run code in a separate thread. I then get a handle to the main thread and dismiss the spinner which works and then i show a UIAlertView. The UIAlertView loads fine however i can not click any of the buttons. If the alert view is outside of the dispatch block it works fine. Any ideas?</p>
  
  <pre><code>[MBProgressHUD showHUDAddedTo:self.view animated:YES];
  dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
  
      // Do something...
      GamePlayManager *gameManager = [GamePlayManager alloc];
      Session *sess = [Session sharedInstance];
  
      //Add the last actor to the end of the list
      NSMutableDictionary *connections = sess.connections;
  
      [connections setObject:sess.secondActor forKey:[NSString stringWithFormat:@"%d",kLastFieldtag]];
  
      BOOL result = [gameManager areAnswersCorrect:sess.connections startingActor:sess.firstActor endingActor:sess.secondActor];
      NSString *display = @"Sorry incorrect. Please recheck your answers.";
  
      UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Result"
                                                      message:display
                                                     delegate:self
                                            cancelButtonTitle:@"Cancel"
                                            otherButtonTitles:@"OK", nil];
  
      if (result)
      {
          display = @"You are correct! You Won!";
  
          if (sess.isMutiplayerGame)
          {
              [_gameCenterController endGame];
  
              [self showGameOverScreen:YES isMultiplayer:YES];
          } 
          else
          {                
              [self showGameOverScreen:YES isMultiplayer:NO];
          }
  
          dispatch_async(dispatch_get_main_queue(), ^{
              [MBProgressHUD hideHUDForView:self.view animated:YES];
  
              [alert show];
          });
  
      } 
      else 
      {
          dispatch_async(dispatch_get_main_queue(), ^{
              [MBProgressHUD hideHUDForView:self.view animated:YES];
  
              [alert show];
          });
      }
  });
  </code></pre>