nxml-mode problem

jing validates the instance OK.
nxml-mode.
When I select the schema I get
Internal error at 72 in rng-validation-mode. Wrong type argument: arrayp, 0

Suggestions please.

regards DaveP



Instance:
<doc>
<wrapper>
oneX
</wrapper>
</doc>


Grammar:
<grammar
  xmlns="http://relaxng.org/ns/structure/1.0"
  datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
   <start>
     <ref name="Doc"/>
     </start>


<define name="Doc">
   <element name="doc">
     <ref name="Except"/>
   </element>
</define>

<define name="Except">
<element name="wrapper">
   <data type="token">
     <except>
       <value>one</value>
       <value>two</value>
     </except>
   </data>
</element>
</define>
</grammar>