[TIL ObjC.001];

When a HTTP call out method don't just check for the lack of an error instead check for an error AND check the status code.

NSUInteger statusCode = ((NSHTTPURLResponse *)response).statusCode;
if (!error && statusCode == 200) {
    // magic
    }];

http://stackoverflow.com/questions/23145160/how-do-you-get-the-status-code-from-datataskwithurls-nsurlresponse

http://stackoverflow.com/questions/14692813/nserror-not-being-populated/14693158#14693158