struts报 java.lang.ClassCastException 异常

登陆页面 提交login.do后出现
  java.lang.ClassCastException
 
  org.apache.struts.taglib.html.ErrorsTag.doStartTag(ErrorsTag.java:215)
  org.apache.jsp.login_jsp._jspx_meth_html_errors_1(login_jsp.java:505)
  org.apache.jsp.login_jsp._jspx_meth_html_form_0(login_jsp.java:333)
  org.apache.jsp.login_jsp._jspService(login_jsp.java:135)
  org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
  org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:298)
  org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
  org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
  org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069)
  org.apache.struts.action.RequestProcessor.internalModuleRelativeForward(RequestProcessor.java:1012)
  org.apache.struts.action.RequestProcessor.processValidate(RequestProcessor.java:980)
  org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:255)
  org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
  org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
 

------解决方法--------------------------------------------------------
请检查
  <html:text property="userName" name= "LoginForm" maxlength="17" styleClass="smallInput"/>