Hello *.*

I´m builind my first application in .NET and a friend on mine give an exemple, but when I build the project, this message ocurrs:

The type or namespace name 'Xml' does not exist in the namespace 'System.Security.Cryptography' (are you missing an assembly reference?)

these are the "using" commands:

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Xml;
using System.Xml.Schema;
using System.Windows.Forms;
using System.Security.Cryptography.Xml;
using System.Security.Cryptography.X509Certificates;

When I try retype the command the intelinsense don´t show the option "Xml" at System.Security.Cryptography

What can I do to inset this namespace ?

thank you all!!!

Frederico