在eclipse下做了struts一个应用出现错误。是怎么回事？

本人模仿书中的例了在eclipse下做了struts一个应用。  多次运行成功了。可是几天后再来运行就出现了以下错误。  在这期间并没有改动，这是怎么回事？    type   Exception   report    message      description   The   server   encountered   an   internal   error   ()  that   prevented   it   from   fulfilling   this   request.    exception       javax.servlet.ServletException:   BeanUtils.populate      org.apache.struts.util.RequestUtils.populate(RequestUtils.java:1254)      org.apache.struts.action.RequestProcessor.processPopulate(RequestProcessor.java:821)      org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:254)      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:709)      javax.servlet.http.HttpServlet.service(HttpServlet.java:802)      sun.reflect.NativeMethodAccessorImpl.invoke0(Native   Method)      sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)      sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)      java.lang.reflect.Method.invoke(Method.java:585)      org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:243)      java.security.AccessController.doPrivileged(Native   Method)      javax.security.auth.Subject.doAsPrivileged(Subject.java:517)      org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:275)      org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:161)      root   cause       java.security.AccessControlException:   access   denied   (java.lang.RuntimePermission   accessDeclaredMembers)      java.security.AccessControlContext.checkPermission(AccessControlContext.java:264)      java.security.AccessController.checkPermission(AccessController.java:427)      java.lang.SecurityManager.checkPermission(SecurityManager.java:532)      java.lang.SecurityManager.checkMemberAccess(SecurityManager.java:1662)      java.lang.Class.checkMemberAccess(Class.java:2125)      java.lang.Class.getDeclaredMethods(Class.java:1762)      org.(MappedPropertyDescriptor.java:386)      java.security.AccessController.doPrivileged(Native   Method)      org.(MappedPropertyDescriptor.java:383)      org.(MappedPropertyDescriptor.java:453)      org.(MappedPropertyDescriptor.java:527)      org.  (MappedPropertyDescriptor.java:149)      org.(PropertyUtils.java:907)      org.(BeanUtils.java:934)      org.(BeanUtils.java:808)      org.apache.struts.util.RequestUtils.populate(RequestUtils.java:1252)      org.apache.struts.action.RequestProcessor.processPopulate(RequestProcessor.java:821)      org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:254)      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:709)      javax.servlet.http.HttpServlet.service(HttpServlet.java:802)      sun.reflect.NativeMethodAccessorImpl.invoke0(Native   Method)      sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)      sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)      java.lang.reflect.Method.invoke(Method.java:585)      org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:243)      java.security.AccessController.doPrivileged(Native   Method)      javax.security.auth.Subject.doAsPrivileged(Subject.java:517)      org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:275)      org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:161)      note   The   full   stack   trace   of   the   root   cause   is   available   in   the   Apache   Tomcat/5.5.17   logs.