open-xchange-groupware daemon dies after a few hours, NullPointerException

[goofy]

hi open-xchange experts,

we are experiencing stability problems with the open-xchange daemon here at the moment so i was wondering if anyone here can help.

ox runs fine after being restarted, but seems to fail after a while. then, when i try to log in, i get a 503 error response (service temporarily not available). i investigated the situation a little further, this is what i found:

# /etc/init.d/open-xchange-groupware status
Checking for service open-xchange-groupware daemon [dead] [FAILED]

apparently the java process has died. apache complains

[Fri Mar 27 14:57:59 2009] [error] (111)Connection refused: proxy: AJP: attempt to connect to 127.0.0.1:8009
(127.0.0.1) failed
[Fri Mar 27 14:57:59 2009] [error] ap_proxy_connect_backend disabling worker for (127.0.0.1)
[Fri Mar 27 14:57:59 2009] [error] proxy: AJP: failed to make connection to backend: 127.0.0.1

in the open-xchange.log.0 i see lots of these:

Mar 27, 2009 2:14:16 PM com.openexchange.ajax.AJAXServlet service
SEVERE: null
java.lang.NullPointerException
at com.openexchange.groupware.calendar.CachedCalendar Iterator.getPreFilledResult(CachedCalendarIterator .java:256)
at com.openexchange.groupware.calendar.CachedCalendar Iterator.next(CachedCalendarIterator.java:154)
at com.openexchange.groupware.calendar.CachedCalendar Iterator.next(CachedCalendarIterator.java:80)
at com.openexchange.ajax.request.AppointmentRequest.a ctionList(AppointmentRequest.java:536)
at com.openexchange.ajax.request.AppointmentRequest.a ction(AppointmentRequest.java:204)
at com.openexchange.ajax.Appointment.doPut(Appointmen t.java:167)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:619)
at com.openexchange.ajax.AJAXServlet.service(AJAXServ let.java:380)
at com.openexchange.ajax.SessionServlet.service(Sessi onServlet.java:152)
at com.openexchange.ajax.PermissionServlet.service(Pe rmissionServlet.java:98)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:689)
at com.openexchange.ajp13.AJPv13RequestHandler.doServ letService(AJPv13RequestHandler.java:575)
at com.openexchange.ajp13.AJPv13Request.response(AJPv 13Request.java:108)
at com.openexchange.ajp13.AJPv13RequestHandler.create Response(AJPv13RequestHandler.java:385)
at com.openexchange.ajp13.AJPv13Connection.createResp onse(AJPv13Connection.java:192)
at com.openexchange.ajp13.AJPv13Listener.run(AJPv13Li stener.java:245)
at java.lang.Thread.run(Thread.java:595)
Mar 27, 2009 2:14:16 PM com.openexchange.ajp13.AJPv13Listener run
SEVERE: null
javax.servlet.ServletException
at com.openexchange.ajax.AJAXServlet.service(AJAXServ let.java:385)
at com.openexchange.ajax.SessionServlet.service(Sessi onServlet.java:152)
at com.openexchange.ajax.PermissionServlet.service(Pe rmissionServlet.java:98)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:689)
at com.openexchange.ajp13.AJPv13RequestHandler.doServ letService(AJPv13RequestHandler.java:575)
at com.openexchange.ajp13.AJPv13Request.response(AJPv 13Request.java:108)
at com.openexchange.ajp13.AJPv13RequestHandler.create Response(AJPv13RequestHandler.java:385)
at com.openexchange.ajp13.AJPv13Connection.createResp onse(AJPv13Connection.java:192)
at com.openexchange.ajp13.AJPv13Listener.run(AJPv13Li stener.java:245)
at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.NullPointerException
at com.openexchange.groupware.calendar.CachedCalendar Iterator.getPreFilledResult(CachedCalendarIterator .java:256)
at com.openexchange.groupware.calendar.CachedCalendar Iterator.next(CachedCalendarIterator.java:154)
at com.openexchange.groupware.calendar.CachedCalendar Iterator.next(CachedCalendarIterator.java:80)
at com.openexchange.ajax.request.AppointmentRequest.a ctionList(AppointmentRequest.java:536)
at com.openexchange.ajax.request.AppointmentRequest.a ction(AppointmentRequest.java:204)
at com.openexchange.ajax.Appointment.doPut(Appointmen t.java:167)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:619)
at com.openexchange.ajax.AJAXServlet.service(AJAXServ let.java:380)
... 9 more

some information on our installation

- CentOS 5.2
- ox Build: 6.8.0-6802, 2009-02-12 16:55:30

any help would be appreciated.

thanks in advance and keep up the good work,

guenter