title: EXC_BAD_ACCESS error for -timeIntervalSinceNow
body: <p>Hoping someone can help with this. I keep getting a bad access error when trying to use the <code>-timeIntervalSinceNow</code> method. I have a variable in this class called <code>NSDate *startDate</code> and I've added <code>@property (nonatomic, retain) NSDate *startDate;</code></p>
  
  <p><code>startDate</code> is used in the code here:</p>
  
  <pre><code>    startDate = [NSDate date];
      updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.1 
                                                     target:self
                                                   selector:@selector(updatePlaybackPosition:)
                                                   userInfo:nil
                                                    repeats:YES];
  }
  </code></pre>
  
  <p>}</p>
  
  <pre><code>- (void)updatePlaybackPosition:(NSTimer *)timer {
     NSTimeInterval interval = [startDate timeIntervalSinceNow];
  </code></pre>
  
  <p>When the program reaches  <code>[startDate timeIntervalSinceNow]</code> it gives a bad access error. From the other posts I've read on this topic, the answer usually seems to have something to do with retaining the date. So, I'm not sure what I'm missing. Any help would be much appreciated! </p>