We are getting below error when we try to click same link twice or doing some action before present action is complete. please help.

04 Aug 2010 03:57:55,919 404221612 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... C_CATEGORY
04 Aug 2010 03:57:56,394 404222087 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... FOCUS_AREA
04 Aug 2010 03:57:56,862 404222555 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... PER_FAMILY
04 Aug 2010 03:57:57,399 404223092 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... T_TECH_GRP
04 Aug 2010 03:57:57,778 404223471 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... UCT_FAMILY
04 Aug 2010 03:58:00,673 404226366 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... M_CATEGORY
04 Aug 2010 03:58:00,832 404226525 INFO [STDOUT] (Thread-83:) Invoking urlhttp://usildaml.ca.com:3590/tops/twb ... =RESP_EXEC
04 Aug 2010 03:58:00,957 404226650 INFO [STDOUT] (Thread-83:) **********CacheManager ReInit END*******
04 Aug 2010 04:00:28,741 404374434 ERROR [STDERR] (Thread-148:) Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@ef0a29 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@9bdf8 [ acquireIncrement -> 1, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, idleConnectionTestPeriod -> 100, initialPoolSize -> 10, maxIdleTime -> 100, maxPoolSize -> 10, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 10, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@8fecc7 [ description -> null, driverClass -> null, factoryClassLocation -> null, jdbcUrl -> jdbc:ingres://USILDB12-QA:II7/olp, properties -> {user=******, password=******} ] , preferredTestQuery -> null, propertyCycle -> 300, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, usesTraditionalReflectiveProxies -> false ] , factoryClassLocation -> null, numHelperThreads -> 3, poolOwnerIdentityToken -> ef0a29 ]
04 Aug 2010 04:00:29,130 404374823 ERROR [STDERR] (Thread-35:) %%%% Error Creating SessionFactory %%%%
04 Aug 2010 04:00:29,165 404374858 ERROR [STDERR] (Thread-35:) org.hibernate.MappingException: Could not read mappings from resource: com/ca/epmis/ValueObjects/PacklistSku.hbm.xml
at org.hibernate.cfg.Configuration.addResource(Configuration.java:485)
at org.hibernate.cfg.Configuration.parseMappingElement(Configuration.java:1465)
at org.hibernate.cfg.Configuration.parseSessionFactory(Configuration.java:1433)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1414)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1390)
at org.hibernate.cfg.Configuration.configure(Configuration.java:1310)
at com.ca.epmis.DAO.HibernateSessionFactory.rebuildSessionFactory(HibernateSessionFactory.java:63)
at com.ca.epmis.DAO.HibernateSessionFactory.getSession(HibernateSessionFactory.java:42)
at com.ca.epmis.BusinessObjects.SearchSKUInputBO.getSkuTypeList(SearchSKUInputBO.java:219)
at com.ca.epmis.Action.CreateSKUAction.execute(CreateSKUAction.java:54)
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.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.jboss.web.tomcat.security.JBossSecurityMgrRealm.invoke(JBossSecurityMgrRealm.java:220)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.jboss.web.tomcat.tc4.statistics.ContainerStatsValve.invoke(ContainerStatsValve.java:76)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:65)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:577)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:263)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:360)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:604)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:562)
at org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:679)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:534)
Caused by: org.hibernate.DuplicateMappingException: Duplicate class/entity mapping com.ca.epmis.ValueObjects.PacklistSku
at org.hibernate.cfg.Mappings.addClass(Mappings.java:118)
at org.hibernate.cfg.HbmBinder.bindRoot(HbmBinder.java:154)
at org.hibernate.cfg.Configuration.add(Configuration.java:386)
at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:427)
at org.hibernate.cfg.Configuration.addResource(Configuration.java:482)
... 56 more
04 Aug 2010 04:00:29,166 404374859 INFO [STDOUT] (Thread-35:) got connection
04 Aug 2010 04:00:29,168 404374861 INFO [STDOUT] (Thread-35:) 04:00:29,167 ERROR [SearchSKUInputBO] Exception occured in getSkuTypeList method:java.lang.NullPointerException
04 Aug 2010 04:00:29,168 404374861 INFO [STDOUT] (Thread-35:) 04:00:29,168 ERROR [CreateSKUAction] Exception occured in createSKUAction:java.lang.NullPointerException
04 Aug 2010 04:00:38,592 404384285 INFO [STDOUT] (Thread-148:) in else part
04 Aug 2010 04:00:41,184 404386877 INFO [STDOUT] (Thread-148:) got connection