Here's my launch file:

<launch>
    <machine name="mal" address="mal" />
    <node name="talker" pkg="rospy_tutorials" type="talker.py" machine="mal" />
</launch>

Here's the output.

started roslaunch server http://harris1:34739/
remote[mal-0] starting roslaunch
remote[mal-0]: creating ssh connection to mal:22
remote[mal-0]: ssh connection created
[mal-0] process has died
remote roslaunch failed to launch: mal

Full log file available here

This is running electric on the core machine (harris1, a PR2) over the PR2's wireless. Mal is running both diamondback and electric. An equivalent result is obtained when ros-root and ros-package-path are set.

<machine name="mal" address="mal" ros-root="/opt/ros/electric/ros/" ros-package-path="/home/dlu/wu-robotics:/opt/ros/electric/stacks" />

Why does the remote roslaunch fail to launch