Ansible Timeout (12s) waiting for privilege escalation prompt

I'm having trouble running my Ansible playbook on AWS instance. Here is my version:

$ ansible --versionansible 2.0.0.2

I created an inventory file as:

[my_ec2_instance]default ansible_host=MY_EC2_ADDRESS ansible_user='ubuntu' ansible_ssh_private_key_file='/home/MY_USER/MY_KEYS/MY_KEY.pem'

Testing connection to my server:

$ ansible -i provisioner/inventory my_ec2_instance -m pingdefault | SUCCESS => {"changed": false, "ping": "pong"}

Now when running my playbook on this inventory I get the error Timeout (12s) waiting for privilege escalation prompt as follows:

$ ansible-playbook -i provisioner/inventory -l my_ec2_instance provisioner/playbook.ymlPLAY [Ubuntu14/Python3/Postgres/Nginx/Gunicorn/Django stack] *****TASK [setup] *******************************************************************fatal: [default]: FAILED! => {"failed": true, "msg": "ERROR! Timeout (12s) waiting for privilege escalation prompt: "}NO MORE HOSTS LEFT *************************************************************PLAY RECAP *********************************************************************default                    : ok=0    changed=0    unreachable=0    failed=1

If I run the same playbook using the .vagrant/provisioners/ansible/inventory/vagrant_ansible_inventory as the inventory parameter it works perfectly on my Vagrant instance.(I believe, proving there is nothing wrong in the playbook/roles itself)

Also, if I run it with an -vvvv, copy the exec ssh line and run it manually it indeed connects to AWS without problems.

Do I need to add any other parameter on my inventory file to connect an EC2 instance? What am I missing?