by Patrick Pollet.
@andrew
the operation get_my_module grade (and the related get_my_quiz_grade, get_my_assignment_grade...) were indeed broken due to confusion between course's module id and instance id. You have to send if activity id, as it appear is the URL, like you did. Internally my code should have used this id to get the course module instance and use that instanceid to fetch grades ...
A revised version tested against Moodle 2.4.3 is on github https://github.com/patrickpollet/moodlews with also minor revisions to get_my_courses due to database changes in Moodle 2.4 and PHP strict standard errors when Moodle was in full debug mode and 'display errors onscreen' activated.
Cheers.