Relation fields in ArrowDB Appcelerator

Question

Anyone have knowledge about relations and ArrowDB? I'm adding a User object as an relation field to a Message object, and that works fine. But when I try to add an relation to a File object from the same Message object I get the following error:

400: Failed to send message: Invalid ACS type: file

Anyone have a clue?

Maybe I'm using the wrong notation for the File object!? I've tried: [ACS_File], [ACS_Files] without any luck?....[ACS_User] works like a charm?

Here is my code:

Cloud.Messages.create({
    to_ids: to.join(','),
    body: 'New Message',
    subject: 'Test Message',
    custom_fields:
    {
    "[ACS_File]file_id":videoFile,
    "[ACS_User]owner_id":to.join(','),

    "pausedAt" : pausedAt,
    "correctAnswer": correctAnswer,
    "a2" : a2,
    "a3" : a3
    }
}, function (e) {
    if (e.success) {
        var message = e.messages[0];
        alert('Success:\n' +
            'id: ' + message.id + '\n' +
            'subject: ' + message.subject + '\n' +
            'body: ' + message.body + '\n' +
            'updated_at: ' + message.updated_at);
            //Her gikk alt bra og melding og video er lastet opp. På tide å sende en push :-)


    } else {
        alert('Error:\n' +
            ((e.error && e.message) || JSON.stringify(e)));
    }
});
}