:D
Finally found the problem... they've changed the defaults in the way XSLT is allowed to create files etc. listed as a 'bug' ( have a read of https://bugs.php.net/bug.php?id=54446 ).
I've changed the code to be
$xp = new XsltProcessor();
//if you want to write from within the XSLT
if (version_compare(PHP_VERSION,'5.4',"<")) {
$oldval = ini_set("xsl.security_prefs",0);
} else {
$oldval = $xp->setSecurityPreferences(0);
}
$xsl = new DOMDocument();
$xsl->load("./GenModelClass.xsl");
$xp->importStylesheet($xsl);
And it now works.
Thanks for you help