How do I get the contact person name from a saleorder

I am getting the contactpersoncode from the saleorder using

ContactPersonCode = salesorder.ContactPersonCode

this is a text number '31'

but as there is onle one contact person on the bus Partner record I get an exeption when using

  oBpEmp = oBP.ContactEmployees
  oBpEmp.SetCurrentLine(CInt(ContactPersonCode) - 1)

Am I using this code correctly? any pointers?