sudo not working when user defined as part of a group

Ubuntu 14.04
Ansible 1.9.1

When I explicitly define a user in the sudoers file, ansible works as expected.

But, when I remove that user from the sudoers file, and add it to the UNIX
group sudo (with `%sudo ALL=(ALL:ALL) ALL` in the sudoers file), the user on
the host is still able to sudo, but the same ansible playbook is now returning
(assuming username yves):

    yves is not in the sudoers file. This incident will be reported.

Any idea what's going on?

Works now, I had not checked the instructions and had not realised there were
git submodules. I have run `git submodule update --init --recursive` and it
solved all my issues.