ERROR: Model Parsing the xml failed

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Hello,

I am trying to create urdf file for the UR5 arm with the Barrett Hand end-effector. I have created this file:

<?xml version="1.0"?>
<robot xmlns:xacro="http://wiki.ros.org/xacro" name="ur5_bh" >
  <!-- include urdfs -->
  <xacro:include filename="$(find ur_description)/urdf/ur5.urdf.xacro"/>
  <xacro:include filename="$(find barret_hand_description)/urdf/bh280.urdf.xacro" />

  <!-- create the robot + bh combo itself as a macro -->
  <xacro:macro name="ur5_with_bh" params="prefix">

    <!-- instantiate -->
    <xacro:ur5 prefix="${prefix}robot_" />
    <xacro:bh      prefix="${prefix}ee_" />

    <!-- attach eef to M-10iA model -->
    <!-- Note: this assumes that the 'bh' macro defines a 'base_link'
        link which is the start of it's kinematic chain (if any) -->
      <!-- tool0 frame -->
  <link name="tool0" />
  <joint name="ee_tool" type="fixed">
    <parent link="_base_link"/>
    <child link="tool0"/>
    <origin xyz="0.0 0.0 0.0205" rpy="0.0 ${-pi/2} 0.0"/>
  </joint>

  </xacro:macro>
</robot>

When I run "check_urdf /home/ros/cats_ws/src/universal_robot/ur_bh/src/ur5_barret.urdf.xacro" It return this error:

Error:   No link elements found in urdf file
         at line 180 in /build/buildd/urdfdom-0.2.10+dfsg/urdf_parser/src/model.cpp
ERROR: Model Parsing the xml faile

Does anybody know how to solve this problem?