RLException: Machine [ubuntu2] already added and does not match duplicate entry

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I have had a working multi-machine environment for a while but today I get this error that I cannot debug myself.

RLException: Machine [ubuntu2] already added and does not match duplicate entry

I have set the following environment variables:

Machine 1 ubuntu1:

export ROS_MASTER_URI=http://10.0.0.2:11311
export ROS_IP=10.0.0.1
export ROS_HOSTNAME=10.0.0.1

Machine 2 ubuntu2:

export ROS_MASTER_URI=http://localhost:11311
export ROS_IP=10.0.0.2
export ROS_HOSTNAME=10.0.0.2

In my launch file, I declare machine like:

<machine name="ubuntu2" address="10.0.0.2" env-loader="/home/ubuntu/catkin_ws/src/env.sh" user="ubuntu"/>

Machine 2 runs the roscore master node. The namespaces resolves in ssh (ssh ubuntu2). Machine1 runs the launch files. I am not sure what do to fix this.