Combo Box Populating

In my code I have a ddl that when seelcted should load the combo box, however nothing happens?
<asp:ComboBox ID="cbUserName" runat="server" AppendDataBoundItems="True" DropDownStyle="DropDownList" MaxLength="10" > </asp:ComboBox> Protected Sub ddlAcctNum_SelectedIndexChanged(sender As Object, e As System.EventArgs) Handles ddlAcctNum.SelectedIndexChanged If ddlAcctNum.SelectedIndex <> 0 Then GETUSERNAMES() 'GETUSERINFO() End If End Sub Public Sub GETUSERNAMES() SqlUsrMaint.SelectCommand = "SELECT ACCTNUM, USERNAME" & _ " FROM FTPUsers WHERE ACCTNUM='" & ddlAcctNum.Text & "'" Dim dv As DataView = CType(SqlUsrMaint.Select(DataSourceSelectA ...