Opera 9 XSLT error - Call to undefined function: docum

Using Opera 9.02 (8585) on Windows 2000, JRE v1.5, I get
XSLT processing failed!
Error: invalid expression: document('Lookup.xml')
Call to undefined function: document

The stylesheet works without error in TransforMiiX and MSXML3;
the statements in question are:
<xsl:for-each select="document('Lookup.xml')">
  <xsl:value-of select="key('url', $result/URL)/@neu"/>
</xsl:for-each>