xsl:include error in excel 2010

I have an xml file which refers to a file1.xsl file. In there I have to refere to a second file2.xsl.
When I open the xml file in excel 2003 it's no problem and everything is working fine.
If I open it in excel 2010 I get a parse error. My syntax should be correct, and if I manually include the content of file2 into file1 it's also working.
Any ideas?

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:variable name="vStyleSheet" select="'file1.xsl'"/>
<xsl:include href="file2.xsl"/>
<xsl:template name="css-style"><style type="text/css">

I've been looking around and it seems like the <xsl:include is no longer supported in excel2010.
I'm giving up and will focus to combining the two *.xsl files into one.

@Mod's, should I mark it 'solved' even though it's not?

No, leaved it unsolved. Maybe someone will respond, even if only to confirm your findings.