CorporateTaxOverrd and DepositCorporateTaxOverrd

I'm having problems using VI to update Sales Order and Invoice files that contain the following fields: CorporateTaxOverrd and DepositCorporateTaxOverrd. These fields appear blank in older records and all set to "N" in newer records, but I can't find much info on exactly what these fields are used for, how they get set, and why my VI jobs crash.

Any information that anybody knows about these fields would be greatly appreciated. Thanks in advance.