Retrieving value from combo box?

Question

I have a databound combo box in the sub page_load that I'm trying to get the value from but keep getting this error.
Object reference not set to an instance of an object.
I have a button click event that I need to retrieve this value so that when its clicked a datagrid will be created based on the selected value. Any help is greatly appreciated.
Connection Code and data binding!
Public Sub Page_Load(sender as Object, e as EventArgs)
    '1. Create a connection
    Dim myConnection as SQLconnection
    'Dim myConnection as New SqlConnection(ConfigurationSettings.AppSettings("connectionString"))
 myConnection = New SQLconnection("server=xxxx; database=xxxx; uid=xxxx; pwd=xxxx")
    '2. Create the command object, passing in the SQL string
    Const strSQL as String = "SELECT DISTINCT Prov FROM OPPE_Clinic"
    Dim myCommand as New SqlCommand(strSQL, myConnection)
    '3. Create the DataReader
 myConnection.Open()
 
 Dim objDR as SqlDataReader
 objDR = myCommand.ExecuteReader(CommandBehavior.CloseConnection)
 
 'Databind the DataReader to the listbox Web control
 practName.DataSource = objDR
 practName.DataBind()
 
 'Add a new listitem to the beginning of the listitemcollection
 practName.Items.Insert(0, new ListItem("-- Select Provider --"))
  End Sub
Button Click event I'm trying to retrieve the combo box value with.
 
  Public Sub Submit_Click(ByVal sender As Object, ByVal e As System.EventArgs)
   
 Dim submit As Button
 Dim pracText As TextBox
 pracText.text = practName.SelectedItem.text
 
  End Sub
<form name="form1" runat="server">
<table border=0 bgcolor="#F9F9F2" height=455 width=900>
  <tr>
    <td><asp:listbox id="practName" runat="server" Rows="1" DataTextField="Prov" AutoPostBack="True" />&nbsp;&nbsp;<asp:textbox id="pracText" runat="server" Width="100" />&nbsp;&nbsp;<asp:Button id="submit" runat="server" Text="Submit" OnClick="Submit_Click" />
 </td>
  </tr>
</table>
</form>