[MonoDevelop] problem compiling with monodevelop

[ponto]

i'm starting to use monodevelop and c#.

i was testing xml tools,
and with this code:

// project created on 18-11-2007 at 23:17
using System.Xml;
using System;

namespace xmlteste
{
	
	class MainClass
	{
		public static void Main(string[] args)
		{
			//Console.WriteLine("Hello World!");
			string url="http://ws.audioscrobbler.com/1.0/user/o_ponto/profile.xml";
			using (XmlReader reader = XmlReader.Create(url))
			{
				
			        while (reader.Read())
			        {
			            switch (reader.NodeType)
			            {
			                case XmlNodeType.Element:
			                    Console.Write("<{0}>", reader.Name);
			                    break;
			            }
			        }
			}
		}
		
	}
}

when i compile using gmcs all works well.

but when using monodevelop with runtime 2.0,
gives me this:
Type=Error, Priority=Normal, Description=The type or namespace name
`System.Xml' could not be found. Are you missing a using directive or
an assembly reference?(CS0246)

how can i solve this?