title: Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed using AFNetworking
body: <p>I am using AFNetworking library to post data on server using POST method.</p>
  
  <p>Following is my code</p>
  
  <pre><code>- (void) callLoginAPI:(NSDictionary *)dictProfile{
      // 1
      NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:[dictProfile valueForKey:@"name"], @"username",
                                                                      [dictProfile valueForKey:@"first_name"],@"first_name",
                                                                      [dictProfile valueForKey:@"last_name"],@"last_name",
                                                                      [dictProfile valueForKey:@"email"],@"email",
                                                                      [dictProfile valueForKey:@"birthday"],@"dob",
                                                                      [dictProfile valueForKey:@"gender"],@"gender",
                                                                      [[dictProfile valueForKey:@"location"] valueForKey:@"name"],@"location",
                                                                      [dictProfile valueForKey:@"timezone"],@"timezone",
                                                                      @"",@"language",
                                                                      [NSString stringWithFormat:@"http://graph.facebook.com/%@/picture?type=large",[dictProfile valueForKey:@"id"]],@"profile_pic_url",
                                                                      @"",@"cover_pic_url",nil];
  
  
  
      AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
      manager.requestSerializer = [AFJSONRequestSerializer serializer];
  
  
  
      [manager POST:@"http://10.1.81.35:8000/api/login/" parameters:params success:^(AFHTTPRequestOperation *operation, id responseObject) {
          NSLog(@"JSON: %@", responseObject);
      } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
          NSLog(@"Error: %@", error);
      }];
  }
  </code></pre>
  
  <p>but I got following error in response</p>
  
  <pre><code>Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (JSON text did not start with array or object and option to allow fragments not set.) UserInfo=0x797f2620 {NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}
  </code></pre>
  
  <p>I can't understand what is the problem with the code.</p>