Need help with (recursive) xsd group

I have this xsd:

<?xml version="1.0" encoding="utf-8" ?>
<xs:schema xmlns="http://myschema.com/schema"
           targetNamespace="http://myschema.com/schema"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:complexType name="aType" mixed="true">
        <xs:group ref="aElements" minOccurs="0" maxOccurs="unbounded"/>
    </xs:complexType>

    <xs:group name="aElements">
        <xs:choice>
            <xs:element name="a" type="aType"/>
        </xs:choice>
    </xs:group>

    <xs:element name="b">
        <xs:complexType>
            <xs:choice minOccurs="0" maxOccurs="unbounded">
                <xs:group ref="aElements"/>
            </xs:choice>
        </xs:complexType>
    </xs:element>
</xs:schema>

and I try to validate this xml document against it:

<?xml version="1.0" encoding="utf-8" ?>
<b xmlns="http://myschema.com/schema">
    <a/>
</b>

However, Visual Studio 2008's xml validator complains about the <a> element:

The element 'b' in namespace 'http://myschema.com/schema' has invalid child element 'a' in namespace 'http://myschema.com/schema'. List of possible elements expected: 'a'.

What is the problem?

Edit: Oops, when dumbing down the example I caused forgot to make the element optional inside the element, causing infinite recursion. The problem is still there with this mod, though.

---

ANSWER: The answer was that the xs:schema tag should include the elementFormDefault="qualified" attribute.

From stackoverflow

• you define aElements with aType, and aType with aElements. i'm not an xsd expert, but how is that supposed to work?

  erikkallen : Oops, the element was meant to be optioal. Q updated.

• You could make your life much easier using an editor for XSD development. We've been using Liquid XML Studio for ages, it makes life much easer.

  Ilja Preuß : not an answer to the question