dwr的报错问题

org.directwebremoting.extend.MarshallException: Error marshalling com.lsp.model.User: Max depth exceeded when dereferencing c0-e1. See the logs for more details.
at org.directwebremoting.convert.BasicObjectConverter.convertInbound(BasicObjectConverter.java:151)
at org.directwebremoting.dwrp.DefaultConverterManager.convertInbound(DefaultConverterManager.java:159)
at org.directwebremoting.dwrp.BaseCallMarshaller.marshallInbound(BaseCallMarshaller.java:155)
at org.directwebremoting.servlet.PlainCallHandler.handle(PlainCallHandler.java:44)
at org.directwebremoting.servlet.UrlProcessor.handle(UrlProcessor.java:101)
at org.directwebremoting.servlet.DwrServlet.doPost(DwrServlet.java:146)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:201)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:163)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:108)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:402)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:249)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:267)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:245)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:260)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.IllegalStateException: Max depth exceeded when dereferencing c0-e1
at org.directwebremoting.extend.InboundVariable.attemptDereference(InboundVariable.java:72)
at org.directwebremoting.extend.InboundVariable.<init>(InboundVariable.java:41)
at org.directwebremoting.convert.BasicObjectConverter.convertInbound(BasicObjectConverter.java:136)
... 22 more

web.xml:
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>uk.ltd.getahead.dwr.DWRServlet</servlet-class>
<init-param>
<param-name>debug</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>crossDomainSessionSecurity</param-name>
<param-value>false</param-value>
</init-param>
<init-param>
<param-name>mconfig-yonghu</param-name>
<param-value>/WEB-INF/dwr.xml</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>dwr-invoker</servlet-name>
<url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
</web-app>

dwr.xml:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://www.getahead.ltd.uk/dwr/dwr20.dtd">
<dwr>
 <allow>
  <create creator="new" javascript="DWRUserAccess">
  <param name="class" value="com.lsp.DWR.DWRUserAccess" />
  </create>
  <convert match="com.lsp.model.User" converter="bean"/>  
 </allow>
</dwr>