Hi Russell,

It could just be that your have a dodgy cdx. You might have tried these things before but you could :-

-Verify your DBC.
-Reindex your table.
-Delete the offending cdx and reindex the related table to create a new cdx.
-Use a third party product i.e. fuctionality found in FoxFix will check the validity of a table before you open it and fix it if need be this pre-empting corruption.

Good Luck
Rob