place your message in a page with this header :
<meta http-equiv="refresh" content="5;url=Default.aspx" />
and redirect them to this page.
This header will redirect them to the "default.aspx" after 5 seconds but before that they can see your message.
example :
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Access Denied</title>
<meta http-equiv="refresh" content="5;url=Default.aspx" />
<link rel="Stylesheet" type="text/css" href="default.css" />
</head>
<body dir="rtl">
<form id="form1" runat="server">
<div class="error">
<img alt="error" src="images\cross1.png" width=50 height=50 />
access denied.</div>
<br />
<br />
<a href="Default.aspx">go to home page</a>
</form>
</body>