title: Core Data Error - NSDate localizedCaseInsensitiveCompare: unrecognised selector sent to instance
body: <p>I have searched for the last several hours but have yet to find an answer. I implemented an AVFoundation camera, Im saving the image data to disk and storing only the path in core data. Everything works fine but after a random number of taken photos I get this error:</p>
  
  <p>CoreData: error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  -[__NSDate localizedCaseInsensitiveCompare:]: unrecognized selector sent to instance</p>
  
  <p>This is my fetch request code:</p>
  
  <pre><code>NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Photo"];
  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"notebook = %@", notebookItem];
  [request setPredicate:predicate];
  request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"dateTaken"
                                                                ascending:NO
                                                                 selector:@selector(compare:)]];
  </code></pre>
  
  <p>And here is how I save the data in a separate class:</p>
  
  <pre><code>//I create a photo Object to save to core data and set properties like dateTaken and tittle
  
  //Here is where I create the path name
  NSDate *dateString = [[NSDate alloc] init];
  NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
  [formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS"];
  NSString *path = [formatter stringFromDate:dateString];
  
  //Now I save to disk
  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentsDirectory = [paths objectAtIndex:0];
  // the path to write file
  NSString *filePath = [documentsDirectory stringByAppendingPathComponent:path];
  NSLog(@"path: %@", path);
  [[[self captureManager] ImageDataObject] writeToFile:filePath atomically:YES];
  
  photo.imagePath = filePath;
  
  [notebookItem addPhotosObject:photo];
  [self.SharedDocumentHandlerInstance saveDocument];
  </code></pre>
  
  <p>I tracked down the point of crash and it occurs in the line of code where I save the document (the last one above) but maybe the fetch request is the one that causes it. I also set self.fetchedResultsController.delegate = nil in my table. And again, this error occurs after a random number of photos is taken. Thanks for any help in advance!</p>