XML Parsing Error: prefix not bound to a namespace

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Hello all,

I'm getting a parsing error with my urdf when I try to run it. it says the error comes from this line <controller:gazebo_ros_time name="gazebo_ros_time" plugin="libgazebo_ros_time.so">

This is the console error upon launch:

Traceback (most recent call last):
  File "/opt/ros/fuerte/stacks/xacro/xacro.py", line 35, in <module>
    xacro.main()
  File "/opt/ros/fuerte/stacks/xacro/src/xacro.py", line 542, in main
    doc = parse(f)
  File "/usr/lib/python2.7/xml/dom/minidom.py", line 1920, in parse
    return expatbuilder.parse(file)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 928, in parse
    result = builder.parseFile(file)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 207, in parseFile
    parser.Parse(buffer, 0)
xml.parsers.expat.ExpatError: unbound prefix: line 795, column 6
Invalid <param> tag: Cannot load command parameter [robot_description]: command [/opt/ros/fuerte/stacks/xacro/xacro.py '/Martin/ros_workspace/learning_urdf/H20_urdf.urdf'] returned with code [1]. 

Param xml is <param command="$(find xacro)/xacro.py '$(find learning_urdf)/H20_urdf.urdf'" name="robot_description"/>

Here is the whole code:

    <gazebo>
     <controller:gazebo_ros_time name="gazebo_ros_time" plugin="libgazebo_ros_time.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>1000.0</updateRate>
        <interface:audio name="dummy_gazebo_ros_time_iface_should_not_be_here"/>
      </controller:gazebo_ros_time>

      <!-- PR2_ACTARRAY -->
      <controller:gazebo_ros_controller_manager name="gazebo_ros_controller_manager" plugin="libgazebo_ros_controller_manager.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>1000.0</updateRate>
        <interface:audio name="gazebo_ros_controller_manager_dummy_iface" />
      </controller:gazebo_ros_controller_manager>
    <turnGravityOff>true</turnGravityOff>

  </gazebo>

EDIT: This code does work when I try to launch this with the gazebo simulator but when I try to launch it with my warehouse planning launch file it gives this crash. Does it have to do with using different time? My warehouse launch file uses But the urdf file specifies this <controller:gazebo_ros_time name="gazebo_ros_time" plugin="libgazebo_ros_time.so">

Hope someone can help, thanks in advance!

Kind Regards, Martin