How to enable Moodle Mobile App for all accounts

Just wondering if anyone who has got the Moodle Mobile App (v2.2) to work with their Moodle site know what I'm doing wrong?

I have enabled the Webservices on my Moodle Site as per the Moodle Doc for enabling the Moodle Mobile App.

I as a site administrator can login to the App with no issues

When I try to log in as any other user (student, teacher or Manager) it throws the error message "Invalid response value detected"

Any help with this would be much appreciated!

Thanks,
Nathan