"Root Element is Missing" error trying to add XSD schema to Word

I'm working my way through the book "VSTO for Mere Mortals", which introduces people with a VBA background to Visual Studio and VB.Net.

One of the examples involves adding an XSD schema to Word, but it won't load. I get the message "Root element is missing". Here it is:


<?xml version="1.0" encoding="utf-8" ?>
<xs:schema targetNamespace=
      "http://schemas.microsoft.com/vsto/samples"
      elementFormDefault="qualified"
      xmlns="http://schemas.microsoft.com/vsto/samples"
      xmlns:mstns="http://schemas.microsoft.com/vsto/samples"
      xmlns:xs="http://www.w3.org/2001/XMLSchema">

      <xs:element name="Letter" type="LetterType"></xs:element>
      <xs:complexType name="LetterType">
            <xs:all>
                  <xs:element name="Address" type="AddressType"
                        minOccurs="0" maxOccurs="1" />
                  <xs:element name="Content" type="ContentType"
                        minOccurs="0" maxOccurs="1" />
            </xs:all>
      </xs:complexType>
      <xs:complexType name="AddressType">
            <xs:sequence>
                  <xs:element name="Author" type="xs:string"
                        minOccurs="0" maxOccurs="1" />
                  <xs:element name="Addressee" type="xs:string"
                        minOccurs="0" maxOccurs="1" />
                  <xs:element name="Re" type="xs:string" minOccurs="0"
                        maxOccurs="1" />
            </xs:sequence>
      </xs:complexType>
      <xs:complexType name="ContentType">
            <xs:sequence>
                  <xs:element name="Salutation" type="xs:string"
                        minOccurs="0" maxOccurs="1" />
                  <xs:element name="Body" type="xs:string"
                        minOccurs="0" maxOccurs="1" />
                  <xs:element name="Closing" type="xs:string"
                        minOccurs="0" maxOccurs="1" />
            </xs:sequence>
      </xs:complexType>
</xs:schema>