I have an XML document which looks like
<folder>
  <link author="ME"/ url="something">
  <link author="YOU" url="something else"/>
  <folder>
    <link author="ME"/ url="something">
    <folder>
     <link author="ME"/ url="something">
     <link author="YOU" url="something else"/>
   </folder>
 </folder>
</folder>

There can be any number of depths of folders and there can be any
number of authors.


What I want to do is parse the XML and return another XML document with

the applicable links and structure


My XSL looks like
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema" version="1.0">
<xsl:param name="Filter" select="'default value'"/>
<xsl:template match="node() | @* | / | root">
  <xsl:copy>
            <xsl:apply-templates select="node() | @*" />
</xsl:copy>
</xsl:template>
<xsl:template match='treenode[@Author=$Filter]' />
</xsl:stylesheet>


The desired outcome would be if I pass "YOU in as a filter I get
<folder>
   <link author="YOU" url="something else"/>
  <folder>
      <folder>
         <link author="YOU" url="something else"/>
     </folder>
 </folder>
</folder>


I am using the .NET System.XMl space to do the prcessing
The problem is I get an error from the treenode[@... line saying
invalid key pattern.  It either has a variable reference or key
function. 


Any ideas how I can fix this?