i checked with taxes' post and it works

so what you do wrong is setting valuemember and displaymemeber for each row
here is the right code
instead of :
VB Code:
  1. For Each myRow In myTable.Rows

  2.         cmbSurname.ValueMember = myRow("EmployeeID")

  3.         cmbSurname.DisplayMember = myRow("Surname")

  4.         cmbSurname.Items.Add(myRow("Surname"))

  5.     Next

use
VB Code:
  1. cbsurname.datasource = mydataset.tables("Employees")

  2. cbsurname.valuemember = "EmpoyeeId"

  3. cbsurname.displaymember = "Surname"