Joint_state_publisher syntax error in urdf_tutorial

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I am trying to follow the urdf tutorial found at /wiki/urdf/Tutorials/Building a Visual Robot Model with URDF from Scratch (sorrie can't post links)

But whenever I try to start the display of the first model using:

roslaunch urdf_tutorial display.launch model:=01-myfirst.urdf

Rviz crashes. In order to find my problem I tried to start everything manually, but when I run rosrun joint_state_publisher joint_state_publisher _robot_description:=01-myfirst.urdf. I get the following error:

Traceback (most recent call last):
  File "/opt/ros/groovy/stacks/robot_model_visualization/joint_state_publisher/joint_state_publisher", line 202, in <module>
    jsp = JointStatePublisher()
  File "/opt/ros/groovy/stacks/robot_model_visualization/joint_state_publisher/joint_state_publisher", line 25, in __init__
    robot = xml.dom.minidom.parseString(description).getElementsByTagName('robot')[0]
  File "/usr/lib/python2.7/xml/dom/minidom.py", line 1931, in parseString
    return expatbuilder.parseString(string)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 940, in parseString
    return builder.parseString(string)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 223, in parseString
    parser.Parse(string, True)
xml.parsers.expat.ExpatError: syntax error: line 1, column 0

I haven't been able to find this syntax error, as I am directly using the xml file from the tutorial page.

I am using Groovy on Ubuntu 13.04.

Does someone know how to fix this?