Select Statement Using Multi-list Box Values For WHERE IN SQL Clause

I have a gridview that is based on the selection(s) in a listbox.  The gridview renders fine if I only select one value from the listbox.  I recive this error though when I select more that one value from the listbox:

Syntax error converting the nvarchar value '4,1' to a column of data type int.  If, however, I hard code 4,1 in place of @ListSelection (see below selectCommand WHERE and IN Clauses) the gridview renders perfectly.

<asp:SqlDataSource ID="SqlDataSourceAll" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"

SelectCommand="SELECT DISTINCT dbo.Contacts.Title, dbo.Contacts.FirstName, dbo.Contacts.MI, dbo.Contacts.LastName, dbo.Contacts.Suffix, dbo.Contacts.Dear, dbo.Contacts.Honorific, dbo.Contacts.Address, dbo.Contacts.Address2, dbo.Contacts.City, dbo.Contacts.StateOrProvince, dbo.Contacts.PostalCode FROM dbo.Contacts INNER JOIN dbo.tblListSelection ON dbo.Contacts.ContactID = dbo.tblListSelection.contactID INNER JOIN dbo.ListDescriptions ON dbo.tblListSelection.selListID = dbo.ListDescriptions.ID WHERE (dbo.tblListSelection.selListID IN (@ListSelection)) AND (dbo.Contacts.StateOrProvince LIKE '%') ORDER BY dbo.Contacts.LastName">

<SelectParameters>

<asp:Parameter Name="ListSelection" DefaultValue="1"/>

</SelectParameters>

</asp:SqlDataSource>

The selListID column is type integer in the database.

I'm using the ListBox1_selectedIndexChanged in the code behind like this where I've tried using setting my selectparameter using the label1.text value and the Requst.From(ListBox1.UniqueID) value with the same result:

 

Protected Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

Dim Item As ListItem

For Each Item In ListBox1.Items

If Item.Selected Then

If Label1.Text <> "" Then

Label1.Text = Label1.Text + Item.Value + ","

Else

Label1.Text = Item.Value + ","

End If

End If

Next

Label1.Text = Label1.Text.TrimEnd(",")

SqlDataSourceAll.SelectParameters("ListSelection").DefaultValue = Request.Form(ListBox1.UniqueID)

End Sub

What am I doing wrong here?  Thanks!