asp.net update pane will not fire event - asp.net

Question

I am trying to implement an update panel on my web page. when I add this, everything works fine:
<script runat="server">
Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Me.Label2.Text = Date.Now.ToString
End Sub
</script>
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<fieldset>
<asp:Label ID="label1" runat="server" Text="Label"></asp:Label>
<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
<asp:Label ID="Label2" runat="server" Text="Label"></asp:Label>
<asp:Button ID="Button2" runat="server" Text="Button" />
</fieldset>
</ContentTemplate>
</asp:UpdatePanel>
<asp:TextBox ID="TextBox1" runat="server" Height="289px" TextMode="MultiLine"
Width="663px" ReadOnly="True"></asp:TextBox>
The problem comes when I try to do some stuff on the on_load event of the application. in the code behind, i try to do this:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles Me.Load
If Not IsPostBack Then
....a function that produces a very long xml string
Me.TextBox1.Text ="<f"
End If
End Sub
This will cause the event to not occur. If i change the "<" from the string, all is well. why cant I have "<" in my strings? This is important because i wont allow me to put an xml string in the text box.
any help would be great!

Answer 1

Try using &lt< rather than <