Ecco questa è la pagina sceglilegale.aspx la parte dei due DropDownList

codice:
<div id="legale1">
<ASP:Textbox id="lblstr_IdLegaleAffid" runat="server"></ASP:Textbox>
    </div>  
<div id="legale2">
Categoria: 
    <asp:DropDownList 
ID="categoriaList" 
DataTextField="DescrCategoria" 
DataValueField="IDcategoria"
OnSelectedIndexChanged="catelistChange" 
runat="server" />
Specializzazione: 
    <asp:DropDownList 
ID="specializzazioneList" 
DataTextField="DescrSpecializzazione" DataValueField="IDspecializzazione" 
runat="server" >
    </asp:DropDownList>
Questa la pagina con il code-behind
codice:
   Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack Then
'Popolo il primo dropdownlist

 Dim MyConnection07 As OleDbConnection
                MyConnection07 = New OleDbConnection("Provider=SQLOLEDB; Data Source=ESCZ-NA-00; Integrated Security=SSPI; Initial Catalog=ContenziosoEsattoriale")
                MyConnection07.Open()
                Dim strSQL07 As String = "SELECT IDCategoria, DescrCategoria FROM TabcategoriaProf"
                Dim objCommand07 As New OleDbCommand(strSQL07, MyConnection07)
                Dim objDataReader07 As OleDbDataReader
                objDataReader07 = objCommand07.ExecuteReader(CommandBehavior.CloseConnection)
                categoriaList.DataSource = objDataReader07
                categoriaList.DataTextField = "DescrCategoria"
                categoriaList.DataValueField = "IDCategoria"
                categoriaList.DataBind()
                Validate()
end if

'popolo il secondo dropdownlist 

 Protected Sub cateListChange(ByVal sender As Object, ByVal e As System.EventArgs) Handles categoriaList.SelectedIndexChanged

        'Dim lbl_dropdown1 As String = Me.categoriaList.SelectedValue()
        Dim lbl_dropdown1 As String = categoriaList.Items(categoriaList.SelectedIndex).Value
        Dim MyConnection08 As OleDbConnection
        MyConnection08 = New OleDbConnection("Provider=SQLOLEDB; Data Source=ESCZ-NA-00; Integrated Security=SSPI; Initial Catalog=ContenziosoEsattoriale")
        MyConnection08.Open()
        Dim strSQL08 As String = "SELECT IdSpecializzazione, DescrSpecializ FROM TabSpecializzazione Where IdCategoria = " & lbl_dropdown1
        Dim objCommand08 As New OleDbCommand(strSQL08, MyConnection08)
        Dim objDataReader08 As OleDbDataReader
        objDataReader08 = objCommand08.ExecuteReader(CommandBehavior.CloseConnection)
        specializzazioneList.DataSource = objDataReader08
        specializzazioneList.DataTextField = "DescrSpecializ"
        specializzazioneList.DataValueField = "IdSpecializzazione"
        specializzazioneList.DataBind()
        Validate()

    End Sub

Grazie