title: NSTimer not firing the selector
body: <p>In ios5.0 with ARC, in my rootviewcontroller I call a method in a security manager object that is held by the app delegate. In that method I setup the timer as below</p>
  
  <pre><code>NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self 
                                         selector:@selector(updateModel:) userInfo:str repeats:YES];
  [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes]; 
  </code></pre>
  
  <p>However, this never fires the selector ie. updateModel: never gets called. What may be wrong? Is there another more efficient way I can do this without using NStimer?</p>