Fab not finding host key

Thank you for taking the time to look at my post.

I have a django site up and running, and I am trying to run a command on the remote (ubuntu) host from my local (windows) computer via fab. I have set the env.key_filename, but every time I run a command I am prompted for the user's password.

Does anyone have any suggestions?

Fab Snippet:

env.key_filename = "path\to\key.ppk"
env.no_keys = True
env.name = 'testing'
env.user = 'ubuntu'
env.project_name = 'PROJECT'
env.project_root = '/home/%(user)s/venvs/%(name)s/%(project_name)s/' % env
env.host_string = 'myIp'
env.branch = 'master'
env.venv = 'source /home/%(user)s/venvs/%(name)s/bin/activate && ' % env

Console:

>fab testing install_requirements
[myIp] run: source /home/ubuntu/venvs/test开发者_运维问答ing/bin/activate &&  pip install -r requirements.txt
Password for ubuntu@myIP:

Looks to me like Fabric issue #265. You should use an OpenSSH key, not a .ppk.