ZCS 8.0 on SLES11 SP2. Frequently, mail crashes. zmcontrol status shows zmmailboxd not running. A look into the log/mailbox shows:
2012-11-11 19:11:14,722 INFO [qtp1415079679-282:http://127.0.0.1:8080/service/soap/AuthRequest] [name=user@domain.com;oip=ip.add.re.ss;ua=zclient/8.0.0_GA_5434;] SoapEngine - handler exception
com.zimbra.common.service.ServiceException: auth credentials have expired
ExceptionId:qtp1415079679-282:http://127.0.0.1:8080/service/soap/A...fc828562402a94
Code:service.AUTH_EXPIRED
at com.zimbra.common.service.ServiceException.AUTH_EX PIRED(ServiceException.java:296)
at com.zimbra.common.service.ServiceException.AUTH_EX PIRED(ServiceException.java:300)
at com.zimbra.cs.service.AuthProvider.validateAuthTok en(AuthProvider.java:594)
at com.zimbra.cs.service.account.Auth.handle(Auth.jav a:106)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:421)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:284)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:157)
at com.zimbra.soap.SoapServlet.doWork(SoapServlet.jav a:290)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:206)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:727)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:208)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:820)
at org.eclipse.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:565)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1361)
at com.zimbra.cs.servlet.SetHeaderFilter.doFilter(Set HeaderFilter.java:57)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1332)
at org.eclipse.jetty.servlets.UserAgentFilter.doFilte r(UserAgentFilter.java:77)
at org.eclipse.jetty.servlets.GzipFilter.doFilter(Gzi pFilter.java:218)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1332)
at org.eclipse.jetty.servlets.DoSFilter.doFilterChain (DoSFilter.java:464)
at org.eclipse.jetty.servlets.DoSFilter.doFilter(DoSF ilter.java:327)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1332)
at org.eclipse.jetty.servlet.ServletHandler.doHandle( ServletHandler.java:477)
at org.eclipse.jetty.server.handler.ScopedHandler.han dle(ScopedHandler.java:119)
at org.eclipse.jetty.security.SecurityHandler.handle( SecurityHandler.java:524)
at org.eclipse.jetty.server.session.SessionHandler.do Handle(SessionHandler.java:227)
at org.eclipse.jetty.server.handler.ContextHandler.do Handle(ContextHandler.java:1031)
at org.eclipse.jetty.servlet.ServletHandler.doScope(S ervletHandler.java:406)
at org.eclipse.jetty.server.session.SessionHandler.do Scope(SessionHandler.java:186)
at org.eclipse.jetty.server.handler.ContextHandler.do Scope(ContextHandler.java:965)
at org.eclipse.jetty.server.handler.ScopedHandler.han dle(ScopedHandler.java:117)
at org.eclipse.jetty.server.handler.ContextHandlerCol lection.handle(ContextHandlerCollection.java:250)
at org.eclipse.jetty.server.handler.HandlerCollection .handle(HandlerCollection.java:149)
at org.eclipse.jetty.server.handler.HandlerWrapper.ha ndle(HandlerWrapper.java:111)
at org.eclipse.jetty.rewrite.handler.RewriteHandler.h andle(RewriteHandler.java:312)
at org.eclipse.jetty.server.handler.DebugHandler.hand le(DebugHandler.java:77)
at org.eclipse.jetty.server.handler.HandlerWrapper.ha ndle(HandlerWrapper.java:111)
at org.eclipse.jetty.server.Server.handle(Server.java :349)
at org.eclipse.jetty.server.AbstractHttpConnection.ha ndleRequest(AbstractHttpConnection.java:452)
at org.eclipse.jetty.server.AbstractHttpConnection.co ntent(AbstractHttpConnection.java:894)
at org.eclipse.jetty.server.AbstractHttpConnection$Re questHandler.content(AbstractHttpConnection.java:9 48)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpPa rser.java:857)
at org.eclipse.jetty.http.HttpParser.parseAvailable(H ttpParser.java:235)
at org.eclipse.jetty.server.AsyncHttpConnection.handl e(AsyncHttpConnection.java:77)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.han dle(SelectChannelEndPoint.java:606)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.r un(SelectChannelEndPoint.java:46)
at org.eclipse.jetty.util.thread.QueuedThreadPool.run Job(QueuedThreadPool.java:603)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.r un(QueuedThreadPool.java:538)
at java.lang.Thread.run(Thread.java:722)

The very next log entry shows:
2012-11-11 19:11:14,733 INFO [qtp1415079679-282:http://127.0.0.1:8080/service/soap/AuthRequest] [name=user@domain.com;oip=ip.add.re.ss;ua=zclient/8.0.0_GA_5434;] soap - AuthRequest elapsed=40
2012-11-11 19:11:14,752 ERROR [qtp1415079679-275:https://192.168.124.3:2443/?loginOp=...er@domain.com] [] webclient - auth credentials have expired
com.zimbra.common.soap.SoapFaultException: auth credentials have expired

It looks like the users session timed out but instead of gracefully asking for credentials/re-login, it crashes ZCS. How do i fix this this?