value of type 'string'

Error from : SQLADR.Update(cmbFrm.SelectedValue, cmbTo.SelectedValue) --> value of type 'string' cannot be converted to 'system.data.dataset.

Protected Sub grdDeptEmp_RowUpdating(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewUpdateEventArgs) Handles grdDeptEmp.RowUpdating
      'To Fetch the data based on the Emp Number and update
      StrQry = "Select FromPeriod,ToPeriod from OtherDeptEmp"
      SQLADR = New SqlDataAdapter(StrQry, Conn)
      Dim cmbFrm As DropDownList = DirectCast(grdDeptEmp.Rows(e.RowIndex).FindControl("cmbFrm"), DropDownList)
      Dim cmbTo As DropDownList = DirectCast(grdDeptEmp.Rows(e.RowIndex).FindControl("cmbTo"), DropDownList)

      'SQLADR.Update(cmbFrm.SelectedValue, cmbTo.SelectedValue, Convert.ToInt32(lblEmpNo.Text))
      SQLADR.Update(cmbFrm.SelectedValue, cmbTo.SelectedValue)
      grdDeptEmp.EditIndex = -1
      FillGrid()

  End Sub