TOMCAT503错误

Apache Tomcat/4.1.34 - Error report

                   HTTP Status 503 - Servlet zkLoader is currently unavailable
     ___________________________________________________________________________________

   type Status report

   message Servlet zkLoader is currently unavailable

   description The requested service (Servlet zkLoader is currently unavailable) is not
   currently available.
     ___________________________________________________________________________________

  Apache Tomcat/4.1.34

网上搜索了半天也没找到个准确解释,那位大虾能指点一下,谢了