BI platform can't work and tomcat services can't stop normally

After our BI platform (BI4.1 sp4) works normally one day, the next day the platform will not able to do fine and we must restart tomcat. Before i restart tomcat, i need stop tomcat services, but "Apache Tomcat for BI 4" always keep the status "stopping". I must stop the services by window's task manager. I check the tomcat error logs stderr.log and find the below information:

SEVERE: Servlet.service() for servlet [equinoxbridgeservlet] in context with path [/BOE] threw exception

java.lang.RuntimeException: org.apache.jasper.JasperException: java.lang.NullPointerException: while trying to invoke the method com.businessobjects.swd.appcontext.CafAppWebSessionContext.getPreferredViewingLocale() of a null object returned from com.businessobjects.swd.appcontext.RequestInfo.getCafAppWebSessionContext()

at com.businessobjects.http.servlet.internal.BundlePathAwareServiceHandler.serviceHelper(BundlePathAwareServiceHandler.java:254)

at com.businessobjects.http.servlet.internal.BundlePathAwareServiceHandler.service(BundlePathAwareServiceHandler.java:197)

at com.businessobjects.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:248)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.eclipse.equinox.servletbridge.BridgeServlet.service(BridgeServlet.java:220)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at com.businessobjects.pinger.TimeoutManagerFilter.doFilter(TimeoutManagerFilter.java:168)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)

at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)

at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)

at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)

at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)

at java.lang.Thread.run(Thread.java:761)

Caused by: org.apache.jasper.JasperException: java.lang.NullPointerException: while trying to invoke the method com.businessobjects.swd.appcontext.CafAppWebSessionContext.getPreferredViewingLocale() of a null object returned from com.businessobjects.swd.appcontext.RequestInfo.getCafAppWebSessionContext()

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.eclipse.equinox.jsp.jasper.JspServlet.service(JspServlet.java:121)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at com.businessobjects.http.servlet.internal.ServletRegistration.service(ServletRegistration.java:110)

at com.businessobjects.http.servlet.internal.ServletLastFilterChainElement.service(ServletLastFilterChainElement.java:30)

at com.businessobjects.http.servlet.internal.filter.FilterChainImpl.doFilter(FilterChainImpl.java:46)

at com.businessobjects.bip.core.web.boetrustguard.BOETrustPrepareFilter.doFilter(BOETrustPrepareFilter.java:35)

at com.businessobjects.http.servlet.internal.FilterRegistration.doFilter(FilterRegistration.java:72)

at com.businessobjects.http.servlet.internal.filter.FilterChainImpl.doFilter(FilterChainImpl.java:43)

at com.businessobjects.bip.core.web.supportabilty.TraceLogScopeFilter.doFilter(TraceLogScopeFilter.java:38)

at com.businessobjects.http.servlet.internal.FilterRegistration.doFilter(FilterRegistration.java:72)

at com.businessobjects.http.servlet.internal.filter.FilterChainImpl.doFilter(FilterChainImpl.java:43)

at com.businessobjects.sdk.actionfilter.WorkflowFilter.doFilter(WorkflowFilter.java:45)

at com.businessobjects.http.servlet.internal.FilterRegistration.doFilter(FilterRegistration.java:72)

at com.businessobjects.http.servlet.internal.filter.FilterChainImpl.doFilter(FilterChainImpl.java:43)

at com.businessobjects.bip.core.web.appcontext.RequestInitFilter.doFilter(RequestInitFilter.java:26)

at com.businessobjects.http.servlet.internal.FilterRegistration.doFilter(FilterRegistration.java:72)

at com.businessobjects.http.servlet.internal.filter.FilterChainImpl.doFilter(FilterChainImpl.java:43)

at com.businessobjects.http.servlet.internal.BundlePathAwareServiceHandler.serviceHelper(BundlePathAwareServiceHandler.java:235)

... 24 more