Expected start or end tag when unmarshalling

I'm currently assessing jsonix as a component for an open souce capability for Enterprise Models visualisation.
From an XML schema, I created the P0 mapping.
I then referenced it for unmarshaling an xml file created according to the schema. But I had the message error indicated in the title.
I tried it with a simpler schema, but had the same error message.
I've difficulties interpreting where the problem comes from.
Error message is the following:
`/Users/nicolasfigay/node_modules/jsonix/jsonix.js:1298
throw new Error('Expected start or end tag.');
^

Error: Expected start or end tag.
at Object.nextTag (/Users/nicolasfigay/node_modules/jsonix/jsonix.js:1298:10)
at Object.unmarshalDocument (/Users/nicolasfigay/node_modules/jsonix/jsonix.js:2129:9)
at /Users/nicolasfigay/node_modules/jsonix/jsonix.js:2099:18
at /Users/nicolasfigay/node_modules/jsonix/jsonix.js:164:8
at Object.handleTransport (/Users/nicolasfigay/node_modules/jsonix/jsonix.js:309:7)
at transport.onreadystatechange (/Users/nicolasfigay/node_modules/jsonix/jsonix.js:298:13)
at dispatchEvent (/Users/nicolasfigay/node_modules/xmlhttprequest/lib/XMLHttpRequest.js:591:25)
at setState (/Users/nicolasfigay/node_modules/xmlhttprequest/lib/XMLHttpRequest.js:610:14)
at handleError (/Users/nicolasfigay/node_modules/xmlhttprequest/lib/XMLHttpRequest.js:532:5)
at ClientRequest.errorHandler (/Users/nicolasfigay/node_modules/xmlhttprequest/lib/XMLHttpRequest.js:459:14)`

Code is the following:
`ar http = require('http');
var fs = require('fs');
var Jsonix = require('jsonix').Jsonix;
var PO = require('./PO.js').PO;

http.createServer(function (req, res) {

// First we construct a Jsonix context - a factory for unmarshaller (parser)
// and marshaller (serializer)
var context = new Jsonix.Context([PO]);

// Then we create a unmarshaller
var unmarshaller = context.createUnmarshaller();

unmarshaller.unmarshalURL('./Model_View.xml',
function (unmarshalled) {
console.log('OK');
});

res.writeHead(200, {'Content-Type': 'text/html'});
res.end('Hello World!');
}).listen(8080);`

Any idea concerning the origin of the error?

Best regards.