Windows Phone xmlDocument.SelectSingleNode Error

Hi i get this error on building out to windows phone 8

System.Xml.XmlNode System.Xml.XmlNode::SelectSingleNode(System.String,System.Xml.XmlNamespaceManager)` doesn’t exist in target framework.

any idea of how to fix this?

 XmlDocument XD = new XmlDocument();
			XmlNamespaceManager mgr=new XmlNamespaceManager(XD.NameTable);
            XD.Load(SR);

			XmlNode SceneNode = XD.SelectSingleNode("/*",mgr);

The Windows Phone support for XML can be read here:

Note that on WP8 and WSA Unity uses MS .Net and not Mono, so the features that are supported can differ compared to platforms where Mono is used. Use the Microsoft documentation for Windows Phone to learn how to use c# features and classes.