Is ECDiffieHellmanCn supported on Windows XP SP2   

I wrote that ECDiffieHellmanCn class (framework 3.5) is supported on Win XP 
SP2:
http://msdn.microsoft.com/en-us/library/system.security.cryptography.ecdiffiehellmancng.aspx

But i have this message when i run the code:

System.PlatformNotSupportedException.

Do i have to install something?

date: Mon, 30 Jun 2008 11:15:01 -0700   author:   PierreRQ