add into a listbox - "Object reference not set to an instance of an object."

[tmashley]

hello

i need to produce a web page that has a button that takes a selected item from "listbox1" and adds it into "listbox2" via a dataset, this application needs to be used by many users at the same time.

this is the code for the button...

    Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        Dim Tag As DataRow
        Tag(1) = ListBox1.SelectedItem.Text
        dstSelectedTags.Tables("tblSelectedTags").Rows.Add(Tag)
        ListBox2.DataSource = dstSelectedTags
        ListBox2.DataBind()
    End Sub 

i am getting "Object reference not set to an instance of an object."

what is wrong??

please help
thanks,
tom