Cannot launch UR5 simulation in gazebo

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I'm attempting to launch a simulation of the UR5 in gazebo with the command roslaunch ur_gazebo ur5.launch. I am getting a number of errors including

ERROR: cannot launch node of type [pr2_mechanism_diagnostics/pr2_mechanism_diagnostics]: pr2_mechanism_diagnostics

and

[ERROR] [1412703963.702016682, 0.508000000]: No p gain specified for pid.  Namespace: /gazebo_ros_control/pid_gains/shoulder_pan_joint

and

[ERROR] [1412703964.014360175, 0.760000000]: Could not find joint 'shoulder_pan_joint' in 'hardware_interface::EffortJointInterface'.
[ERROR] [1412703964.014464269, 0.760000000]: Failed to initialize the controller
[ERROR] [1412703964.014512292, 0.760000000]: Initializing controller 'arm_controller' failed
[ERROR] [WallTime: 1412703965.015916] [1.759000] Failed to load arm_controller

I had previously messed around with the UR5 in simulation around June, and it worked fine (though the PID gains were a bit off). Has anyone else had this problem? Have you figured out how to fix it?