Problem with document() function on web server

I tried two different versions of the document() function to format dates.
Both versions worked on my local hard drive but not on the web server. I
know that I have a more recent version of Xalan on my hard drive, but I am
wondering if something else is causing the problem.
 
This version of the template, in which the monthnames were stored in
separate namespace, caused the stylesheet to stop transforming.
 
 <fr:month-names>
  <fr:month num="01">jan</fr:month>
  <fr:month num="02">f&#233;v</fr:month>
  <fr:month num="03">mar</fr:month>
 </fr:month-names>
 
 <xsl:template name="FrenchMonth">
  <xsl:value-of
select="document('')/*/fr:month-names/fr:month[@num=$month]"/>
 </xsl:template>
 
This version of the template, in which the monthnames were stored in an
external XML file, returned a null value.
 
<MonthNames>
 <French>
  <Name num="01">jan</Name>
  <Name num="02">f&#233;v</Name>
  <Name num="03">mar</Name>
 </French>
</MonthNames>
 
 <xsl:variable name="FrenchMonth"
select="document('month_names.xml')/MonthNames/French"/>
 <xsl:template name="FrenchMonth">
  <xsl:value-of select="$FrenchMonth/Name[@num=$month]"/>
 </xsl:template>
 
Maria