struts 遇上这种错误怎么解决???

HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:370)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.lang.NullPointerException
org.apache.struts.taglib.TagUtils.retrieveMessageResources(TagUtils.java:1219)
org.apache.struts.taglib.TagUtils.message(TagUtils.java:1082)
org.apache.struts.taglib.bean.MessageTag.doStartTag(MessageTag.java:226)
org.apache.jsp.login_jsp._jspx_meth_bean_message_0(org.apache.jsp.login_jsp:167)
org.apache.jsp.login_jsp._jspx_meth_html_html_0(org.apache.jsp.login_jsp:120)
org.apache.jsp.login_jsp._jspService(org.apache.jsp.login_jsp:90)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.12 logs.