diff between direct call and variable call

Is this valid?
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:variable name="styleFile" select="/document/stylesheet/Menu/@XSL"/>
<xsl:include href="$styleFile"/>

cos when I put in the actual file like this:
<xsl:include href="myFile.xsl"/>

it works, yet when I have the variable as the 1st case, it doesn't work?!?!
the browser says:
"The system cannot locate the object specified."
can anyone please throw some light on this?!
Thanx!!

Rosa

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list