我用了jdon的开源论坛,但是论坛经常运行半天以后就报错。大家能不能帮我看看怎么回事? java.lang.ClassCastException: com.jdon.web.UserEnvFront at jsp_servlet._jive.__login._jspService(Ljavax.servlet.http.HttpServletRequest;Ljavax.servlet.http.HttpServletResponse;)V(__login.java:261) at weblogic.servlet.jsp.JspBase.service(Ljavax.servlet.ServletRequest;Ljavax.servlet.ServletResponse;)V(JspBase.java:33) at weblogic.servlet.internal.ServletStubImpl$ServletInvocationAction.run()Ljava.lang.Object;(ServletStubImpl.java:971) at weblogic.servlet.internal.ServletStubImpl.invokeServlet(Ljavax.servlet.ServletRequest;Ljavax.servlet.ServletResponse;Lweblogic.servlet.internal.FilterChainImpl;)V(ServletStubImpl.java:402) at weblogic.servlet.internal.ServletStubImpl.invokeServlet(Ljavax.servlet.ServletRequest;Ljavax.servlet.ServletResponse;)V(ServletStubImpl.java:305) at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.run()Ljava.lang.Object;(WebAppServletContext.java:6350) at weblogic.security.acl.internal.AuthenticatedSubject.doAs(Lweblogic.security.subject.AbstractSubject;Ljava.security.PrivilegedAction;)Ljava.lang.Object;(Optimized Method) at weblogic.security.service.SecurityManager.runAs(Lweblogic.security.acl.internal.AuthenticatedSubject;Lweblogic.security.acl.internal.AuthenticatedSubject;Ljava.security.PrivilegedAction;)Ljava.lang.Object;(SecurityManager.java:118) at weblogic.servlet.internal.WebAppServletContext.invokeServlet(Lweblogic.servlet.internal.ServletRequestImpl;Lweblogic.servlet.internal.ServletResponseImpl;)V(WebAppServletContext.java:3635) at weblogic.servlet.internal.ServletRequestImpl.execute(Lweblogic.kernel.ExecuteThread;)V(ServletRequestImpl.java:2585) at weblogic.kernel.ExecuteThread.execute(Lweblogic.kernel.ExecuteRequest;)V(ExecuteThread.java:197) at weblogic.kernel.ExecuteThread.run()V(ExecuteThread.java:170) at java.lang.Thread.startThreadFromVM(Ljava.lang.Thread;)V(Unknown Source)