MessageBox does not popup if using with Atlas on the web application

[Ted Ngo]

I am try to use the Atlas

Here is my example:
<<atlas:ScriptManager ID="S1" runat="server" />
<div>
<table id=tbl1 runat=server border=0 width=100%>
<tr>
<td width=20% class=lbltxt>
<asp:Label ID=Label1 Text="enter text:"
runat=server></asp:Label>
</td>
<td class=lbltxt>
<asp:TextBox ID=txtSource Width=250px
runat=server></asp:TextBox>
</td>

</tr>

<tr>
<td colspan=2 class=lbltxt>
<asp:Button ID="btnMessage" runat="server"
Text="Submit" />
</td>
</tr>
<table>
</div>

<atlas:UpdatePanel runat="server" id="MyUpdatePannel">
<ContentTemplate>
<asp:Label ID="lblCurrentTime"
runat="server"></asp:Label>
</ContentTemplate>
<Triggers>
<atlas:ControlEventTrigger ControlID=btnMessage
EventName="Click" />
</Triggers>
</atlas:UpdatePanel>

<atlas:UpdateProgress ID="myUpdateProgress" runat=server>
<ProgressTemplate>
<asp:Label Text="please wait" runat="server"
CssClass="Testing"></asp:Label>
</ProgressTemplate>
</atlas:UpdateProgress>

--- Code behind ---

protected void Page_Load(object sender, EventArgs e)
{

txtSource.Focus();

if (Page.IsPostBack)
{
CreatePDF();
}
}

private void CreatePDF()
{
--Message box if empty
if (txtSource.text == "")
{
//Call my message box class to show the message
MessageBox.Show("Please enter text here");
return;
}
else
{
//Do something for me
}
}

if I do not enter text in the textbox and click submit, I message box
does not show up.
If I do not use with Atlase Framework, then it work fine.

Please help.