ERROR with libgazebo_ros_joint_state_plublisher.so

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i have a really small project and i try to run rviz with libgazebo_ros_joint_state_plublisher.so but it is not working. i donot know why someone can help me?

<?xml version="1.0"?>
<robot name="test_bot">
<!-- hier is the base of the Robot-->
<link name="base_link">
    <visual>
        <geometry>
            ,<box size="0.6 0.3 0.1"/>
        </geometry>
        <material name="red">
            ,<color rgba="1 0.0 0.0 1"/>
        </material>
    </visual>
    <!-- this is for the fisical simulation-->
    <collision>
        <geometry>
            ,<box size="0.6 0.3 0.1"/>
        </geometry>
    </collision>
    <!-- inertial it is important because it 
        is that make the Bot move-->
    <inertial>
        <mass value ="1.0"/>
        <inertia ixx="0.015" ixy="0" ixz="0" iyy="0.0375" iyz="0.0" izz="0.0375"/>
    </inertial>    
</link>

<link name="front_caster_of_wheel">
    <visual>
        <geometry>
            <box size="0.1 0.1 0.1" />
        </geometry>
        <material name="green">
            <color rgba ="0.0 0.4 0.0 0.7"/>
        </material>
    </visual>
    <collision>
        <geometry>
            <box size="0.1 0.1 0.1" />
        </geometry>
    </collision>
    <!-- inertial it is important because it 
        is that make the Bot move-->
        <inertial>
            <mass value ="1.0"/>
            <inertia ixx="0.00083" ixy="0" ixz="0" iyy="0.000083" iyz="0.0" izz="0.000167"/>
        </inertial> 
</link>
<!-- it is important to have a joint ever when you have more links-->
<joint name="front_caster_of_wheel_joint" type="continuous">
    <axis xyz="0.0 0.0 1"/>
    <parent link="base_link"/>
    <child link="front_caster_of_wheel"/>
    <origin xyz ="0.3 0.0 0.0" rpy="0.0 0.0 0.0"/>
</joint>

<link name="front_wheel">
    <visual>
        <geometry>
            <cylinder radius="0.035" length="0.05"/>
        </geometry>
        <material name="black">
            <color rgba ="0.0 0.4 0.0 0.7"/>
        </material>
    </visual>
    <collision>
        <geometry>
            <cylinder radius="0.035" length="0.05"/>
        </geometry>
    </collision>
      <!-- inertial it is important because it 
        is that make the Bot move-->
        <inertial>
            <mass value ="1.0"/>
            <inertia ixx="5.1458e-5" ixy="0" ixz="0" iyy="5.1458e-5" iyz="0.0" izz="6.125e-5"/>
        </inertial> 
</link>

<joint name="front_wheel_joint" type="continuous">
    <axis xyz="0.0 0.0 1"/>
    <parent link="front_caster_of_wheel"/>
    <child link="front_wheel"/>
    <origin xyz="0.05 0.0 -0.05" rpy="-1.5708 0.0 0.0"/>
</joint>

<link name="right_wheel">
    <visual>
        <geometry>
            <cylinder radius="0.035" length="0.05"/>
        </geometry>
        <material name="black">
            <color rgba="0.0 0.0 0.0 0.7"></color>
        </material>
    </visual>
    <collision>
        <geometry>
            <cylinder radius="0.035" length="0.05"/>
        </geometry>
    </collision>
      <!-- inertial it is important because it 
        is that make the Bot move-->
        <inertial>
            <mass value ="1.0"/>
            <inertia ixx="5.1458e-5" ixy="0" ixz="0" iyy="5.1458e-5" iyz ...