add a sales person

hi experts,

I want to add a sales person by following code:

SAPbobsCOM.SalesPersons vSLP = (SalesPersons)rma.GetBusinessObject(BoObjectTypes.oSalesPersons);

vSLP.SalesEmployeeName = name;

vSLP.Remarks = comment;

if (vSLP.Add() != 0)

{

sap.GetLastError(out eCode, out err);

}

a error happened: Code: -8016, Object unsupported.

How can a add a sales person without error? thanks...