智商拙计的问题，没有找到为类LoginAction和error找到定义，然后重新去struts.xml去看，我类个去，我居然把result写成了ERROR
<result name="ERROR">/WEB-INF/content/error.jsp</result>
再看看Action类的源代码
/**
* The action execution was a failure.
* Show an error view, possibly asking the
* user to retry entering data.
*/
public static final String ERROR = "error";
把ERROR改回成error，OK，问题解决。