what is the meaning of this this" class is not key value coding-compliant for the key QS1."

NSString *questionString = [[ NSString alloc] initWithFormat:@"%lu",[questions count]];
    int questions = [questionString intValue];
    NSString *answerString = [[NSString alloc] initWithFormat:@"%lu" , [answers count]];
    int answers = [answerString intValue]/3;
    NSString *correctAnswersString = [[NSString alloc] initWithFormat:@"%lu" , [correctAnswers count]];
    int correctAnswers = [correctAnswersString intValue];
    if ((questions = answers) && (questions == correctAnswers)) {
        NSLog(@"Questions, answers and correct answers written");
    }
    else
    {
        NSLog(@"\nWARNING APP WILL CRASH \nSOLUTION: \nCheck if you have the same amount of questions and CORRECT answers, AND if you jave 3 answers for each question!");
        NSLog(@"\nQUESTIONS = %d \nANSWERS = %d (3 tiems more) \nCORRECTANSWERS = %d ", questions , [answerString intValue] , correctAnswers);
    }



}