ASP.Net: Create SELECT from ListBox with multiple selections

<asp:ListBox ID="selSearchProduct" CssClass="narrow_listbox" Font-Name="monospace" Font-Size="8" AppendDataBoundItems="true" runat="server" SelectionMode="Multiple" Rows="5">
</asp:ListBox>

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I'm trying to modify an existing search script in a VB file that concatenates the WHERE portion of a SELECT statement based on the values of fields on the search form.  Currently, the product field is a text box, but the users want the ability to search for multiple products.

The previous code looked like this:

		If (Me.selSearchApplicationType.SelectedValue.Length > 0) Then
			If (sWhere.Length > 0) Then sWhere &= " AND "
			sWhere &= "application like @application"
			Me.sqlGridSource.SelectParameters.Add("application", "%" & Me.selSearchApplicationType.SelectedValue & "%")
		End If
		If (Me.selSearchProduct.SelectedValue.Length > 0) Then
			If (sWhere.Length > 0) Then sWhere &= " AND "
			sWhere &= "product_id like @product"
			Me.sqlGridSource.SelectParameters.Add("product", "%" & Me.selSearchProduct_id.SelectedValue & "%")
		End If

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I need to change this code so I can check for MULTIPLE selected items from a ListBox control (simple select tag: <select id="selSearchProduct" multiple="multiple">), however, I'm having difficulty looping through the collection to create the statement:

		If (Me.selSearchApplicationType.SelectedValue.Length > 0) Then
			If (sWhere.Length > 0) Then sWhere &= " AND "
			sWhere &= "application like @application"
			Me.sqlGridSource.SelectParameters.Add("application", "%" & Me.selSearchApplicationType.SelectedValue & "%")
		End If
		If (Me.selSearchProduct.SelectedValue.Length > 0) Then
			If (sWhere.Length > 0) Then sWhere &= " AND "
			sWhere &= "("
			For Each ProductSelected in Me.selSearchProduct.Items
				sWhere &= "product_id = @product" & ProductSelected.Index
				If (ProductSelected.Index < Me.selSearchProduct.Items.Count) Then
					sWhere &= " OR "
				End If
				Me.sqlGridSource.SelectParameters.Add("product" & ProductSelected.Index, CInt(ProductSelected.Value))
			Next
			sWhere &= ")"
		End If

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It's coming up with no results.  I want the above script to append the WHERE statement in an way that will look like this:

sWhere &= " AND (product_id = @product1 OR product_id = @product2 OR product_id = @product3)"

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so that the end result will be:

sWhere &= " AND (product_id = 13 OR product_id = 52 OR product_id = 20)"

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I can't see anything wrong with the loop above that would be causing it not to get results.  I know the data is there, because I can get results by creating the statement manually.

NOTE: The reason I left "If (Me.selSearchProduct.SelectedValue.Length > 0) Then"  in the statement is because Me.selSearchProduct.Items > 0 causes an error if none were selected.