partial refresh using update panel working with c# code but not with VB

below given VB.net code , not working but if write the same thing in C# it works 

<div>

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>

<asp:Label ID="Label1" runat="Server"></asp:Label>
<br />
<asp:UpdatePanel ID="UpdatePanel1" runat="Server">
<ContentTemplate>
<asp:Label ID="Label2" runat="server"></asp:Label>
<br />
<br />
<asp:Button ID="Button2" runat="server" Text="Click Me Again" OnClick="Button2_Click"/>
</ContentTemplate>
</asp:UpdatePanel>
</div>

Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click
Label2.Text = DateTime.Now.ToString()
End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Label1.Text = DateTime.Now.ToString()

End Sub