I'm having problems calling a .NET method from an XSLT file. What do I have to do in the XSLT to make sure I can call the method?

If I have a class that I would normally refer to in .NET as MyClient.MyProject.Helper, with a static method called GetComments that returned a XPathNodeIterator object, should I be able to call the GetComments method just be doing the following?

<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:Helper="urn:MyClient.MyProject.Helper"

exclude-result-prefixes="msxml umbraco.library Helper">

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

  <xsl:param name="currentPage"/>

  <xsl:template match="/">

<xsl:variable name="comments" select="Helper.GetComments($currentPage/@id)//comment"/>

  </xsl:template>

</xsl:stylesheet>

Currently I'm getting an error - 'Error parsing XSLT file'. If I remove the <xsl:variable  /> tag there is no error.