>The server has crashed about twice in the last 12 months, so is not that important, but if users switch off their pc abnormally without closing out of the app, the problem resufaces.I've noticed that the size of the cdx file becomes 0 bytes when the users dod this, so maybe I can used this to my advantage.

There are steps you can take to help alleviate the corruption when this happens. Use FLUSH, turn off write cache on the server, use data buffering, transactions, and views. In a corporate environment, make the supervisors responsible and charge back time to the dept. that caused the problem. In a consulting situation, I charge my clients three times the normal rate to fix things.