Index Error

I have imported new customer and vendors to their respective tables in Navision (using native Navision database) and I am now getting an “indexing” error when doing a backup. Before I go to the trouble of doing a backup and restoring… Does anyone have any suggestions on how to fix? I get the error when the indexing function is doing the G/L File and the error references the Customer Table and the No. field. One “Navision Expert” suggested taking a copy of the database, exporting the G/L file to a csv, purging the G/L table and then import the G/L csv… Thank you in adavance…