Any ideas/comments/suggestions ??
In your situation which I have been in before I would strongly suggest disabling the auto update which is in the "crond" configuration and just do updates manually so that you can watch it happen. Most likely the file was corrupted because something else tried to access the file while it was being written and caused the DNS server to basically crash. The other option which I used on my own system for a while was to update at about 4AM on Sunday to ensure nothing is accessing the files.
If you are afraid that you might make a mistake. The chances are high that you will never learn anything.