I am sending a Post with object loader and getting this error in output window. FYI, My didFailWithError: delegate never got hit. Not sure why. `objectLoader:didFailWithError:]:` unrecognized selector `sent to class 0x123608` How did i find out what is 0x123608? I set the router in AppDelegate class and Mapping in AppDelegate too. here is a method in my class which inherit RKObjectLoaderDelegate. I am using shared singleton. [[RKObjectManager sharedManager] postObject:review usingBlock:^(RKObjectLoader *loader){ // loader.params=params, loader.objectMapping = [[RKObjectManager sharedManager].mappingProvider objectMappingForClass:[myclass class]]; loader.serializationMIMEType = RKMIMETypeJSON; // We want to send this request as JSON loader.method = RKRequestMethodPOST; loader.serializationMapping = [RKObjectMapping serializationMappingUsingBlock:^(RKObjectMapping* mapping) { [mapping mapAttributes:@"field1", @"field2",@"field3",nil]; }]; loader.targetObject = nil; loader.delegate = self; }]; }