Help in first use of exslt libraries

Here are the opening lines of my stylesheet:

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:date="http://exslt.org/dates-and-times"
  xmlns:func="http://exslt.org/functions">

  <xsl:include href="lib/exslt-dates.xsl" />
  <xsl:include href="lib/exslt/date/functions/difference/date.difference.function.xsl" />


The directory hierarchy reflected in the href attributes of the <xsl:include> elements accurately represents the view from the directory from which I am trying to execute the transformation (command-line MSXSL).

This template called here is in the file called "date.difference.function.xsl":
    <xsl:call-template name="date:difference">
      <xsl:with-param name="start" select="'2004-01-21'" />
      <xsl:with-param name="end" select="'2004-03-15'" />
    </xsl:call-template>
    
The template called here is in the file called "exslt-dates.xsl":
    <xsl:call-template name="date:_add-days">
      <xsl:with-param name="year" select="'2004'" />
      <xsl:with-param name="month" select="'1'" />
      <xsl:with-param name="day" select="'21'" />
      <xsl:with-param name="days" select="'60'" />
    </xsl:call-template>

When I try to execute the transformation with the former template un-remarked, I get this error message:
Error occurred while compiling stylesheet 'C:\Data\CMMI\PMML\cp-html-table.xsl'.

Code:   0x80004005
Named template '{http://exslt.org/dates-and-times}difference' does not exist in the stylesheet.

When I execute the transformation with the former template remarked out, the call to the template in the exslt-dates.xsl file executes normally.

Am I overlooking something simple here? Has anyone got an idea on why the call to the former template fails?

-- 
Charles Knell
[email protected] - email