<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:dctm="http://www.documentum.com"/>

java.lang.UnsopportedOperationException: This Attribute is read only and cannot be changed.

private void update(Document doc, Data d) throws TestException {

	HashMap<String, String> attrs = d.getAttributes();
	Element parent = doc.getRootElement();
	
        for (String s : attrs.keySet()) {
		parent.addAttribute(s, attrs.get(s));
	}
	addNamespaces(parent);
	break;

}
private void addNamespaces(Element elem){

	String[] dctmAttrs = {"testattr1", "testattr2"};
	Attribute a = null;
	Namespace ns = elem.getNamespaceForPrefix("dctm");
	for (String attrname : dctmAttrs){
		a = elem.attribute(attrname);
		if (a != null){
			a.setNamespace(ns); // <-- Эксепшн здесь
		}
	}
}