[Zope] Debugging sudden restarts/reboots/crashes

Hello Zope friends, We've got a sizeable Zope website (~5000 objects) that have recently started to reboot, sometimes as often as every 2-3 minutes. These restarts are random, but triggered by requests (if it's left idle it doesn't restart). What's the best way to debug such reboots? There's nothing in the STUPID_LOG_FILE about the restarts and I can't find a way to increase the debug logging. We're running Zope 2.4.1. Hope someone can help. Bye, -- Bjorn