Json响应错误NSCocoaErrorDomain Code = 3840“字符0周围的值无效” UserInfo = {NSDebugDescription =字符0周围的值无效

Question

请求是：

{
"MyNumber" : "1",
"MyMessage" : "C1LdbQ6MCyPMiYnmM7STZl5gJIROmHdOA\/1EXOwkXWf9jBLvuTyDR092WF29Zctv78kafx0pNBcguV5Cc+u72MmneL\/z2\/O9a9O0I85l0iPG4TZMwS+jVYy2hxZWB8iuI5cnpdF5LreI5T9hFKp5S8HfD4ChCqcrW0R4QAZKrSWhviAIts3MGw3wkw0LdEPK"
}

回应应该是：

D1491810C63C7AB29EAF14CCF90158C5B71F43E0DBCBB44EA4739E3258A7C0FF624045EFEAFE43722481F214AE34D48D6A0787422144C83D1C1E13626ADAD374

代码：

NSURLSessionDataTask *datatask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError  *connectionError)
      {
          if(connectionError)
          {
              NSLog(@"Connection error :%@",connectionError);
              failedBlock (connectionError);
          }
          else
          {                  
              //Here I am getting response
              NSLog(@"Response data is :%@",[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]);                  

              NSError * error = nil;                  

              //Here I am getting error  Error Domain=NSCocoaErrorDomain Code=3840 "Invalid value around character 0." UserInfo={NSDebugDescription=Invalid value around character 0.}

              NSString * responseData = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];

              if(error)
              {
                  failedBlock(connectionError);
              }
              else
              {
                  successBlock (responseData);
              }
          }
      }
];