Error message - unique index created on two different fields

[zyzolus]

I create 2 unique indexes on 2 fields: Field1 and Field2.

What is the way generate custom error message independent of each
field?ex.:
"Duplicate value in Field1" or "Duplicate value in Field2".

If "OnError" event is used (error code 3022 in this case) the same
error
message will be displayed for both fields.

Thank you for response.

OS:win xp
MS Access 2003