How do you convert an event timestamp to an XMP formatted date?

I found out that I can call:

var myTimeStamp = new XMPDateTime(new Date());

which results in:

2015-03-03T22:56:45.558-06:00

This is a date object and not a string. Good so far.

However, when I call my function "mySetXMP" with the following parameters:

mySetXMP("http://ns.adobe.com/xap/1.0/","LCCRevisionTime","LCCRevisionTime", myTimeStamp,"XMPConst.XMPDATE");

function mySetXMP(xmpNS,xmpFieldName,xmpFieldTarget,myValue,myVarType){ 

var myDocument = app.activeDocument;

with(myDocument.metadataPreferences){

var myNewContainer = createContainerItem(xmpNS, xmpFieldName);

setProperty(xmpNS, xmpFieldTarget, myValue, myVarType);

}

}

The script bails out with the setProperty line hilighted in ExtencScript.