Diffie-Hellman cryptographic algorithm is not supported on this platform

I am keep having this problem.
The specified cryptographic algorithm is not supported on this platform. Exception Details: System.PlatformNotSupportedException: The specified cryptographic algorithm is not supported on this platform.
The below is code.  This code were failed on Windows XP Pro SP3 and Windows 2003 Server with 3.5 framework installed on it.



<%@ Page Language="C#" AutoEventWireup="true" %> <%@ Import Namespace="System"%> <%@ Import Namespace="System.Web"%> <%@ Import Namespace="System.Security.Cryptography"%> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/ ...