New to umbraco and xslt.  Built a simple site with both Home (and Home.master template) and ContentPage (and ContentPage.master template) document types based off of Page (and Site.master template) document type.  All non-home page nodes are of ContentPage document type.  Using a simple left nav based in xslt, the home page and the first node, the About page, the left nav looks fine. 

For all other nodes in the left nav, when I go to those pages, the left nav shows an xslt parse error with the output from appending ?umbDebugShowTrace=true to the url showing this error:

"Attribute and namespace nodes cannot be added to the parent element after a text, comment, pi, or sub-element node has already been added."

I read that sometimes using preserve can have this effect, but that's not in my code.  Can anyone tell me what's wrong?  Here is the xslt code:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xsl:stylesheet [
  <!ENTITY nbsp "&#x00A0;">
]>
<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:msxml="urn:schemas-microsoft-com:xslt"
  xmlns:umbraco.library="urn:umbraco.library" xmlns:Exslt.ExsltCommon="urn:Exslt.ExsltCommon" xmlns:Exslt.ExsltDatesAndTimes="urn:Exslt.ExsltDatesAndTimes" xmlns:Exslt.ExsltMath="urn:Exslt.ExsltMath" xmlns:Exslt.ExsltRegularExpressions="urn:Exslt.ExsltRegularExpressions" xmlns:Exslt.ExsltStrings="urn:Exslt.ExsltStrings" xmlns:Exslt.ExsltSets="urn:Exslt.ExsltSets"
  exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings Exslt.ExsltSets ">

  <xsl:output method="xml" omit-xml-declaration="yes"/>
  <xsl:param name="currentPage"/>

  <!-- Input the documenttype you want here -->
  <xsl:variable name="L2" select="1"/>
  <xsl:variable name="L3" select="2"/>

  <xsl:template match="/">
    <!-- The fun starts here -->
    <p id="leftNav">
      <xsl:for-each select="$currentPage/ancestor-or-self::* [@level=$L2]/* [@isDoc and string(sideNavShow) = '1']">
          <xsl:if test="$currentPage/ancestor-or-self::* [@level]/@id = current()/@id">
            <xsl:attribute name="class">
              <xsl:text>active</xsl:text>
            </xsl:attribute>
          </xsl:if>
        <xsl:choose>
          <xsl:when test="position() = last()">
            <br style="0.5em" />
          </xsl:when>
          <xsl:otherwise>
          </xsl:otherwise>
          </xsl:choose>
        <div>
          <a style="text-transform:uppercase;" href="{umbraco.library:NiceUrl(@id)}">
            <xsl:value-of select="@nodeName"/>
          </a><hr /></div><br />
      </xsl:for-each>
    </p>
  </xsl:template>
</xsl:stylesheet>