invalid type error?

I am evaluating XmlBeans to replace some existing code in a project, and I
am getting an error when attempting to validate some xml.  I have modified
the purchase order example to match what I am doing.

We are not using a namespace in our xml, but we still specify a schema to
validate against:

<?xml version="1.0" encoding="UTF-8"?>
<purchase-order
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
  xsi:noNamespaceSchemaLocation="po.xsd">
    <customer>
        <name>Gladys Kravitz</name>
        <address>Anytown, PA</address>
    </customer>
    <date>2003-01-07T14:16:00-05:00</date>
    <line-item>
        <description>Burnham's Celestial Handbook, Vol 1</description>
        <per-unit-ounces>5</per-unit-ounces>
        <price>21.79</price>
        <quantity>2</quantity>
    </line-item>
    <line-item>
        <description>Burnham's Celestial Handbook, Vol 2</description>
        <per-unit-ounces>5</per-unit-ounces>
        <price>19.89</price>
        <quantity>2</quantity>
    </line-item>
<shipper>
        <name>ZipShip</name>
        <per-ounce-rate>0.74</per-ounce-rate>
    </shipper>
</purchase-order>

The schema looks like:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema";
    elementFormDefault="qualified">

    <xs:element name="purchase-order">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="customer" type="customerType"/>
                <xs:element name="date" type="xs:dateTime"/>
                <xs:element name="line-item" type="line-itemType"
minOccurs="0" maxOccurs="unbounded"/>
                <xs:element name="shipper" type="shipperType"
minOccurs="0"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:complexType name="customerType">
        <xs:sequence>
            <xs:element name="name" type="xs:string"/>
            <xs:element name="address" type="xs:string"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="line-itemType">
        <xs:sequence>
            <xs:element name="description" type="xs:string"/>
            <xs:element name="per-unit-ounces" type="xs:decimal"/>
            <xs:element name="price" type="xs:double"/>
            <xs:element name="quantity" type="xs:int"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="shipperType">
        <xs:sequence>
            <xs:element name="name" type="xs:string"/>
            <xs:element name="per-ounce-rate" type="xs:decimal"/>
        </xs:sequence>
    </xs:complexType>
</xs:schema>

I am just using the default XmlObject.Factory to parse the po.xml file and
then calling the validate method on the resulting XmlObject.  On the call to
validate, I get an "Invalid type" error:

Message: Invalid type.
Severity: 0
Line: -1
Location of invalid XML: <purchase-order
xsi:noNamespaceSchemaLocation="po.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>
    <customer>
    ...

What does this mean?  How can I fix/avoid it?  XMLSpy validates both the
schema and xml file without errors.

The document parses without errors, and I can even perform a query against
it using XmlObject.selectPath().

If it helps, here is my code fragment:

    File testFile = new File("c:/development/projects/sandbox/po.xml");
    System.out.println("File exists: " + testFile.exists() + "; " +
testFile.getAbsolutePath());
    XmlObject document = null;
    XmlOptions opts = new XmlOptions();
    ArrayList errorList = new ArrayList();
    opts.setErrorListener(errorList);
    try {
      document = XmlObject.Factory.parse(testFile, opts);
    }
    catch (XmlException e) {
      System.out.println("exception: " + e.getMessage());
      return;
    }
    catch (IOException e) {
      System.out.println("exception: " + e.getMessage());
      return;
    }

    if (errorList.size() != 0) {
      System.out.println("parse errors:");

      for (int i = 0; i < errorList.size(); i++) {
        XmlError error = (XmlError)errorList.get(i);

        System.out.println("\n" + "Message: " + error.getMessage());
        System.out.println("Severity: " + error.getSeverity());
        System.out.println("Line: " + error.getLine());
        System.out.println("Location of invalid XML: " +
            error.getCursorLocation().xmlText() + "\n");
      }

      errorList.clear();
    }

    if (!document.validate(opts)) {
      System.out.println("validation errors:");
      for (int i = 0; i < errorList.size(); i++) {
        XmlError error = (XmlError)errorList.get(i);

        System.out.println("\n" + "Message: " + error.getMessage());
        System.out.println("Severity: " + error.getSeverity());
        System.out.println("Line: " + error.getLine());
        System.out.println("Location of invalid XML: " +
            error.getCursorLocation().xmlText() + "\n");
      }
    }

    String queryExpression =
      "/purchase-order/customer[name='Gladys Kravitz']";

    XmlObject[] productObj = document.selectPath(queryExpression);
    System.out.println(productObj[0]);

Thanks for any understanding you can share here,
-Mark