How do you edit the Mandatory Depth alert

Can anyone explain how to edit the mandatory depth error message?   From the Windows Manager page, we've set the mandatory depth of our Category field to 3, so users would have to select a subcategory below Payroll.

In the Self Service Web interface, when someone neglects to choose a category below Payroll, they get the error that the {Field} has not been filled to its mandatory depth of {value}.   None of our users could figure what this message meant.

Does anyone know of a way we could change this to say something like {Field} needs to include a subcategory or something.