title: -[NSCFString objectAtIndex:]: unrecognized selector
body: <p>I have this little problem I couldn't find in Google: 
  <code>UITableView</code> works fine until I start scrolling.</p>
  
  <pre><code>Error Message: `-[NSCFString objectAtIndex:]: unrecognized selector  sent to instance 0x5f24870 `
  </code></pre>
  
  <p>Method: </p>
  
  <pre><code>- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
  {
      static NSString *MyIdentifier = @"MyIdentifier";    
      UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];     
      if (cell == nil)
      { 
          cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:MyIdentifier] autorelease];
      }   
      // Set up the cell 
      int storyIndex = [indexPath indexAtPosition: [indexPath length]-1];     
      //populate cell
      cell.textLabel.text = [[myArray objectAtIndex: storyIndex] objectForKey: @"subject"]; 
      return cell;    
  }
  </code></pre>
  
  <p>Just guessed that was the "problem"-method... if you need more infos: please tell me :)
  thanks for all your help!</p>
  
  <p>EDIT:
  myArray is just the normal <code>NSArray *myArray</code>
  It's a sorted Array -></p>
  
  <pre><code>   NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"lesson" ascending:YES];
  NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
  myArray = [resultArray sortedArrayUsingDescriptors:sortDescriptors];
  </code></pre>
  
  <p>resultArray (NSMutableArray) is the Result of an XML-Parser.. hope you can see my problem..</p>