Problem using <xsd:all>

Hi list,

I just need to specify <success> AND <failure> both occuring once each (in any
order).  My schema is:

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
	targetNamespace="http://www.intient.com/irukandji"
	xmlns:tasklist="http://www.intient.com/irukandji"
	elementFormDefault="qualified" attributeFormDefault="unqualified">
...
  <xsd:element name="task">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element ref="tasklist:prerequisites" minOccurs="0"
          maxOccurs="1" />
        <xsd:all>
          <xsd:element ref="tasklist:success" minOccurs="1"
            maxOccurs="1" />
          <xsd:element ref="tasklist:failure" minOccurs="1"
            maxOccurs="1" />
        </xsd:all>
      </xsd:sequence>
      <xsd:attribute name="id" type="xsd:string" use="required" />
    </xsd:complexType>
  </xsd:element>
...
</xsd:schema>

When parsing the schema syntax with both eclipse's schema validation and with
Sun's JAXB library, an error is thrown on the <xsd:all> tag.  The exact error is:

"The content of 'sequence' must match (annotation?, (element | group | choice |
sequence | any)*). A problem was found starting at: all."

According to the w3c, all is a valid tag.  Can anyone shed some light on this error?

Thanks,

Paul