W3 XML Schema validation problem

I'm trying to validate an instance of mathml using the XML schema, as 
specified in appendix a 
(http://www.w3.org/TR/2002/WD-MathML2-20021219/appendixa.html#parsing.usingxsd). 
I'm using Xerces-Java 2.4.0, which is their latest release.

I am receiving the following error:

>ERROR in parsing
>   file 
> "file:///c:/webb/work/library/mathml/mathml2/content/constructs.xsd", line 50
>   cos-nonambig: "http://www.w3.org/1998/Math/MathML":cn and 
> "http://www.w3.org/1998/Math/MathML":cn (or elements from their 
> substitution group) violate "Unique Particle Attribution".

I haven't seen any comments on the mailing list regarding XML validation 
difficulties.  Is this a MathML schema problem, or a Xerces problem, or 
have I just missed something?

Below is my XML file:

<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.w3.org/1998/Math/MathML
             http://www.w3.org/Math/XMLSchema/mathml2/mathml2.xsd">
</mml:math>

Thanks,
Webb


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