Error in javascript Call

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" xmlns:js="JavaScript">
<msxsl:script language="JavaScript" implements-prefix="js">
<![CDATA[
function UpperCase(Value)
{
return Value.toUpperCase();
}
 
function Conversione(time)
{
//minuti
var foobar=time % (60); 
// ore
var minutes = Math.floor(time / 60); 
var zero = "";
if (minutes < 10)
{
zero = "0"
}
return time.toConversione();
}

]]>
</msxsl:script>


inside the template I call the javascript function:

<xsl:variable name="durata" select="js:Conversione(150)"/>

or

<xsl:variable name="durata" select="js:Conversione('150')"/>

the error is the same for both the calling:

msxml3.dll (0x80020009)
run-time error od Microsoft Jscript Expected object row = 24, col = 0 
(row moved respect the script block)

But I call in the same way function UpperCase without any error.