No action instance for path /queryPeriodPayOrNot could be created

Question

描述问题先:前段时间做了个小系统,架构jbuilder+tomcat   5.0+mysql,运行良好.昨天,单位又提出了一点需求,需要修改.但出现了如标题的问题.经过尝试,发现凡是新建的action文件都报这个错,在原文件修改,编译后没有问题. 
    在网上查了很久关于这个问题的答复,1.stuts-config.xml的配置肯定没有错,我甚至是用jb构造的.内容: 
        <action   name="queryPayTaxForm"   type="www.aaa.gov.cn.query.queryPeriodPayOrNot"   scope="request"   path="/queryPeriodPayOrNot"> 
            <forward   name="queryPeriodPayOrNotSuc"   path="/shuiyuan/query/queryPeriodPayOrNot.jsp"   /> 
        </action> 
      2.action肯定是继承了struts的action.     action的开始部分: 
        import   org.apache.commons.logging.*; 
        import   org.apache.struts.action.*; 
        public   class   queryPeriodPayOrNot   { 
    public   queryPeriodPayOrNot()   { 
    }     Log   log   =   LogFactory.getLog("thislog"); 
    queryPayTaxForm   paytaxform; 
    Conn   conn   =   new   Conn(); 
    public   ActionForward   execute(ActionMapping   mapping,   ActionForm   form, 
                                                              HttpServletRequest   request, 
                                                              HttpServletResponse   response)   throws   Exception   { 
        paytaxform   =   (queryPayTaxForm)   form; 
      ...   ...     同样如此配置的以前的文件运行没有一点问题.下面是控制台的错误信息: 
严重:   No   action   instance   for   path   /queryPeriodPayOrNot   could   be   created 
java.lang.ClassCastException 
                at   org.apache.struts.action.RequestProcessor.processActionCreate(Request 
Processor.java:282) 
                at   org.apache.struts.action.RequestProcessor.process(RequestProcessor.ja 
va:220) 
                at   org.apache.struts.action.ActionServlet.process(ActionServlet.java:115 
8) 
                at   org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:415)                 at   javax.servlet.http.HttpServlet.service(HttpServlet.java:709) 
                at   javax.servlet.http.HttpServlet.service(HttpServlet.java:802) 
                at   org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl 
icationFilterChain.java:237) 
                at   org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF 
ilterChain.java:157) 
                at   filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilte 
r.java:123) 
                at   org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl 
icationFilterChain.java:186) 
                at   org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF 
ilterChain.java:157) 
                at   org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperV 
alve.java:214) 
                at   org.apache.catalina.core.StandardValveContext.invokeNext(StandardValv 
eContext.java:104) 
                at   org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav 
a:520) 
                at   org.apache.catalina.core.StandardContextValve.invokeInternal(Standard 
ContextValve.java:198) 
                at   org.apache.catalina.core.StandardContextValve.invoke(StandardContextV 
alve.java:152) 
                at   org.apache.catalina.core.StandardValveContext.invokeNext(StandardValv 
eContext.java:104) 
                at   org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav 
a:520) 
                at   org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.j 
ava:137) 
                at   org.apache.catalina.core.StandardValveContext.invokeNext(StandardValv 
eContext.java:104) 
                at   org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.j 
ava:118) 
                at   org.apache.catalina.core.StandardValveContext.invokeNext(StandardValv 
eContext.java:102) 
                at   org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java: 
535) 
                at   org.apache.catalina.core.StandardValveContext.invokeNext(StandardValv 
eContext.java:102) 
                at   org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav 
a:520) 
                at   org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineVal 
ve.java:109) 
                at   org.apache.catalina.core.StandardValveContext.invokeNext(StandardValv 
eContext.java:104) 
                at   org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav 
a:520) 
                at   org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)                 at   org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:16 
0) 
                at   org.apache.coyote.http11.Http11Processor.process(Http11Processor.java 
:799) 
                at   org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.proce 
ssConnection(Http11Protocol.java:705) 
                at   org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java 
:577) 
                at   org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadP 
ool.java:683) 
                at   java.lang.Thread.run(Thread.java:534) 请各位大虾指点啊!!!着急中...