I think DateBk5 was causing Backupman to crash during scheduled backups.

Backupman (1.52b5) was backing-up without a glitch. About 10 days ago, I noted some problems when trying to set an appointment in DateBk5 (5.4a,p7). After that, about every third Backupman backup would crash. I re-installed DateBk5. So far, no more problems with Backupman.

I suppose this is consistent with the reports of others regarding Calendar and BackupMan. The root problem may be with DBk5 or Calendar, but reinstalling DBk5 solved it.