projContext.executeQueryAsync fails - JSOM - Project Server 2013 Online

I'm trying to build a very simple JSOM app using Napa, that would list the projects created, but I'm getting the following exception: 

    Unexpected response from server. The status code of response is '500'. The status text of response is 'Internal Server Error'.

    Microsoft.SharePoint.Client.ResourceNotFoundException
    Cannot find resource for the request ProcessQuery

Here's a piece of my code:

Default.aspx

    ...
    <script type="text/javascript" src="/_layouts/15/sp.runtime.js"></script>
    <script type="text/javascript" src="/_layouts/15/sp.js"></script>
    <script type="text/javascript" src="/_layouts/15/ps.js"></script>
    ...

App.js

    // Declare global variables.
    var projContext;
    var projects;

    $(document).ready(function () {
        SP.SOD.executeOrDelayUntilScriptLoaded(GetProjects, "ps.js");
    });

    // Get the projects collection.
    function GetProjects() {

        // Display a message to the user to show we are reading the projects. 
        $('#spanMessage').text('Reading projects...');

        // Initialize the current client context.
        projContext = PS.ProjectContext.get_current();

        // Get the projects collection.
        projects = projContext.get_projects();

        // Register the request for information that you want to run on the server.
        projContext.load(projects);

        // Run the request on the server.
        projContext.executeQueryAsync(IterateThroughProjects, QueryFailed);
    }

    function IterateThroughProjects(response) {
        // Get the enumerator and iterate through the collection.
        var enumerator = projects.getEnumerator();
        while (enumerator.moveNext()) {
            var project = enumerator.get_current();

            // Get the target project and then check it out. The checkOut function
            // returns the draft version of the project.
            var draftProject = project.checkOut();

            // Specify "true" to also check the project in.
            var publishJob = draftProject.publish(true);

            // Register the job that you want to run on the server and specify the
            // timeout duration and callback function.
            projContext.waitForQueueAsync(publishJob, 30, QueueJobSent);
        }
    }