MySQL未知列'；useranswers.userid'；在ON子句中

我使用以下MySQL代码得到错误"未找到列：1054未知列'useranswers.userid'in'on clause'"

SELECT COUNT(*) FROM kumianswers 
INNER JOIN users on useranswers.userid = users.id 
INNER JOIN kumiquestions on useranswers.questionid = kumiquestions.id 
WHERE login = '".$username."' and users.level <= 3 and categoryid = 1;

有一个表叫"useranswers"，它确实有一个列叫"userid"，还有一个"users"表有一个"id"字段。这是对一行旧代码的修改，确实有效。我们不得不重新制作表格以适应正在开发的新系统。旧的工作代码是。。。。

SELECT COUNT(*) AS total FROM answers
INNER JOIN users on answers.ans_user = users.user_id 
INNER JOIN questions on answers.ans_question = questions.quest_id 
WHERE username = '".$username."' and ans_level <= 3 and quest_type = 1;