hibernate session get 一个实例后 然后修改 update 报SQL insert, update or delete failed (row not found)错误？？盼解

什么意思 。。
报错啊
Hibernate: update weekreport set PrjId=?, Operator=?, WeekNumber=?, BeginDate=?, EndDate=?, CreateDate=?, Description=?, PublishDate=? where WeekReportId=? 
09:44:31,703 ERROR SessionImpl:2343 - Could not synchronize database state with session 
net.sf.hibernate.HibernateException: SQL insert, update or delete failed (row not found) 
at net.sf.hibernate.impl.NonBatchingBatcher.addToBatch(NonBatchingBatcher.java:25) 
at net.sf.hibernate.persister.EntityPersister.update(EntityPersister.java:688) 
at net.sf.hibernate.persister.EntityPersister.update(EntityPersister.java:641) 
at net.sf.hibernate.impl.ScheduledUpdate.execute(ScheduledUpdate.java:52) 
at net.sf.hibernate.impl.SessionImpl.executeAll(SessionImpl.java:2382) 
at net.sf.hibernate.impl.SessionImpl.execute(SessionImpl.java:2336) 
at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2204) 
at net.sf.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:61) 
at com.daheng.pms.util.HibernateUtil.update(HibernateUtil.java:116) 
at com.daheng.pms.weekreport.WeekReportDispatchAction.publish(WeekReportDispatchAction.java:109) 
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.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:270) 
at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:187) 
at org.apache.struts.actions.LookupDispatchAction.execute(LookupDispatchAction.java:150) 
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431) 
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236) 
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196) 
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432) 
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) 
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269) 
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188) 
at com.daheng.pms.http.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:55) 
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215) 
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188) 
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213) 
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172) 
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117) 
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108) 
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174) 
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:875) 
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665) 
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528) 
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81) 
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689) 
at java.lang.Thread.run(Thread.java:595)