关于hibernate解析映射文档的问题

我的hibernate用的是hibernate3的包，文档的DTD配的也是3。0的，为什么有时候可以正常运行，有时启动sessionFactory时出错呢？
信息如下：java.lang.NullPointerExceptionjava.lang.NullPointerException%%%% Error Creating HibernateSessionFactory %%%%
org.hibernate.InvalidMappingException: Could not parse mapping document from resource com/sudytech/ids/hbm/IDMax.hbm.xml
at org.hibernate.cfg.Configuration.addResource(Configuration.java:523)
at org.hibernate.cfg.Configuration.parseMappingElement(Configuration.java:1511)
at org.hibernate.cfg.Configuration.parseSessionFactory(Configuration.java:1479)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1458)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1432)
at org.hibernate.cfg.Configuration.configure(Configuration.java:1352)
at com.sudytech.hibernate.HibernateFactory.currentSession(HibernateFactory.java:60)
at com.sudytech.ids.server.DefaultSSO.getCurrentUser(DefaultSSO.java:355)
at com.sudytech.ids.server.SSOServices.getCurrentUser(SSOServices.java:44)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.axis.providers.java.RPCProvider.invokeMethod(RPCProvider.java:388)
at org.apache.axis.providers.java.RPCProvider.processMessage(RPCProvider.java:283)
at org.apache.axis.providers.java.JavaProvider.invoke(JavaProvider.java:323)
at org.apache.axis.strategies.InvocationStrategy.visit(InvocationStrategy.java:32)
at org.apache.axis.SimpleChain.doVisiting(SimpleChain.java:118)
at org.apache.axis.SimpleChain.invoke(SimpleChain.java:83)
at org.apache.axis.handlers.soap.SOAPService.invoke(SOAPService.java:453)
at org.apache.axis.server.AxisServer.invoke(AxisServer.java:281)
at org.apache.axis.transport.http.AxisServlet.doPost(AxisServlet.java:699)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at org.apache.axis.transport.http.AxisServletBase.service(AxisServletBase.java:327)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:595)
Caused by: org.hibernate.DuplicateMappingException: Duplicate class/entity mapping com.sudytech.ids.hbm.IDMax
at org.hibernate.cfg.Mappings.addClass(Mappings.java:118)
at org.hibernate.cfg.HbmBinder.bindRoot(HbmBinder.java:145)
at org.hibernate.cfg.Configuration.add(Configuration.java:424)
at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:465)
at org.hibernate.cfg.Configuration.addResource(Configuration.java:520)
... 36 more