I've used XSL in .Net for a while now. I'm trying to view a media folder, which works and I can get the item and view the URL, however, when I try and display it as an html element it says

<?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" xmlns:CWS.Twitter="urn:CWS.Twitter" 
 exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings Exslt.ExsltSets CWS.Twitter ">

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

<xsl:param name="currentPage"/>
<xsl:variable name="mediaFolderId" select="number($currentPage/mediaFolderId)" /> 
<xsl:variable name="thumbWidth" select="number(256)" /> 
<xsl:variable name="thumbHeight" select="number(170)" />
<xsl:template match="/">

        <xsl:if test="number($mediaFolderId)">  
            <ul id="gallery"> 
                <xsl:for-each select="umbraco.library:GetMedia($mediaFolderId, true())/Image">
  <xsl:variable name="picFile" select="umbracoFile"/> 
                    <xsl:if test="umbracoFile !=''"> 
   <li> 
   <xsl:element name="a">            
    <xsl:attribute name="href">
     <xsl:value-of select="./umbracoFile" />
    </xsl:attribute>
   </xsl:element>
   </li> 
  </xsl:if>
  </xsl:for-each>
       </ul>
 </xsl:if>
</xsl:template>

</xsl:stylesheet>

Why can't I do:

<xsl:element name="a">            
    <xsl:attribute name="href">
     <xsl:value-of select="./umbracoFile" />
    </xsl:attribute>
   </xsl:element>

to show an element? If I just do the <xsl:value-of select="./umbracoFile"/> I get

• ~/media/361/more-view-thumbnail_1.jpg

SoI know the element is there, I just can't build it (Umbraco in the back end doesn't show any validation errors either)

Any pointers would be great.