Many Cocoa methods use the NSError class in order to provide error feedback about their executions. In order to show the error, just use the code bellow:

 
- (void)logError:(NSError *)error {
    NSArray* detailedErrors = [[error userInfo] objectForKey:NSDetailedErrorsKey];
    if(detailedErrors != nil && [detailedErrors count] > 0) {
        for(NSError* detailedError in detailedErrors) {
            NSLog(@"  DetailedError: %@", [detailedError userInfo]);
        }
    } else {
        NSLog(@"  %@", [error userInfo]);
    }
}