>When updating SQL Server database with a duplicate value in a unique column I get error 1526 (using VFP function
>AERROR(aErrorInf )). This number seems to be specific to SQL Server and not to VFP. Does it change from version to version of SQL? The reason I am asking is I want to "translate" this number into a meaningful message to a user.

AFAIK it's not SQL Server Error, but the error associated with ODBC in VFP, which is not going to change.