Another problem is that Xron seems to trigger its methods as many times as it 'missed' if the server is stopped for a while. Once I experienced this problem with Xron. I think your case is similar to mines, but the crash circunstances, which I've already disscused in another topic, are different:

My zope died, but the Xron method couldn't be completed successfully. Then when Zope tried again to start, xron tried again to trigger the method. But zope died again and so on. In other words, Zope couldn't complete the transaction and thats why Xron couldn't reschedule the method. This is a reason that makes me think about migrating my Xron Methods to the crontab. Regards, Josef