MemoryStream - type or namespace not found

Can someone give me a clue? Here is the beginning of my code. I get a type or namespace not found for MemoryStream.
I look in the object browser and MemoryStream shows up and the constructor MemoryStream() also shows but…

When I am typing in the code, as far as I get is System.IO. (MemoryStream does not show)

using System;
using System.IO;
using System.Collections;
using System.Reflection;
using System.Xml;
using System.Ext.Xml;
using Microsoft.SPOT;
using System.Text;
using System.Runtime.InteropServices;

namespace XMLwriter
{
	public class writeXMLclass
	{
		public void writeXML()
		{
			MemoryStream ms = new MemoryStream();

Check this thread

http://www.tinyclr.com/forum/topic?id=11185

That was it. I just had to add System.IO in the references.

Thanks

You are welcome!