XeCJK issues

This replaces/updates my previous posting about a hyphenation problem. I've solved that (perhaps), but am now having a problem using XeCJK in MikTeX 2.9 (Windows XP, everything in MiKTeX at latest version, formats rebuilt, repository synced). XeCJK seems to be conflicting with the new l3packages.

To reproduce, I created this minimal document:
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%!TEX TS-program = xelatex+makeindex+bibtex
%!TEX encoding = UTF-8 Unicode

\documentclass{article}

\usepackage{xeCJK}

\begin{document}

Some text.

\end{document}
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With XeCJK enabled, I get the following error:
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("C:\Program Files\MiKTeX 2.9\tex\latex\l3packages\xparse\xparse.sty"
! Undefined control sequence.
<argument> \filename 
                     
l.57 ...\filedate}{\fileversion}{\filedescription}
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with XeCJK disabled, no problems.

Lines 56 and 57 of xparse.sty are:

\ProvidesExplPackage
  {\filename}{\filedate}{\fileversion}{\filedescription}

Can anyone else reproduce this? Any clues as to how to overcome it?

Bruce Rusk

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