cant import the XML library into c#

[ninjaben]

Hello

im using a thirdparty code editor and i wihs to use XML in it, ive tried calling: using System.Xml;

using System;
using System.Xml;
using System.Collections;
using Ascentn.Workflow.Base;
 
namespace ManagedCode
{
 
 
    public class CSharpCodeSnippet
    {
        // Invoke method is this class's entry point
        public void Invoke(
            WFProcessInstance pi, 
            WFAutomaticWorkItem w, 
            IWFAPI api, 
            NameValue[] parameters)
        {

but it just spits out the error: The type or namespace name 'Xml' does not exist in the namespace 'System' (are you missing an assembly reference)

Could you help me with this

thanks

Ben