Error while launching model in gazebo

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I have built an urdf file from solidworks and converted the urdf to sdf as below.

 <?xml version='1.0'?>
<sdf version='1.4'>
  <model name='JMbot1'>
    <link name='Base_plate'>
      <pose>0 0 0 0 -0 0</pose>
      <inertial>
        <pose>-0.3317 -0.71959 -0.39019 0 -0 0</pose>
        <mass>0.55378</mass>
        <inertia>
          <ixx>0.0061249</ixx>
          <ixy>0.00016086</ixy>
          <ixz>-8.6651e-18</ixz>
          <iyy>0.0041631</iyy>
          <iyz>-1.4656e-17</iyz>
          <izz>0.010283</izz>
        </inertia>
      </inertial>
      <collision name='Base_plate_collision'>
        <pose>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://JMbot1/meshes/Base_plate.STL</uri>
          </mesh>
        </geometry>
      </collision>
      <visual name='Base_plate_visual'>
        <pose>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://JMbot1/meshes/Base_plate.STL</uri>
          </mesh>
        </geometry>
      </visual>
      <velocity_decay>
        <linear>0</linear>
        <angular>0</angular>
      </velocity_decay>
    </link>
    <link name='Castor_F'>
      <pose>-0.31952 0.39256 -0.57008 -1.5708 1.1481 -6.76601e-16</pose>
      <inertial>
        <pose>2.2204e-16 0 0.031164 0 -0 0</pose>
        <mass>0.056555</mass>
        <inertia>
          <ixx>2.4476e-05</ixx>
          <ixy>-2.8588e-35</ixy>
          <ixz>1.0281e-20</ixz>
          <iyy>2.4476e-05</iyy>
          <iyz>-1.2617e-20</iyz>
          <izz>7.4341e-06</izz>
        </inertia>
      </inertial>
      <collision name='Castor_F_collision'>
        <pose>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://JMbot1/meshes/Castor_F.STL</uri>
          </mesh>
        </geometry>
      </collision>
      <visual name='Castor_F_visual'>
        <pose>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://JMbot1/meshes/Castor_F.STL</uri>
          </mesh>
        </geometry>
      </visual>
      <velocity_decay>
        <linear>0</linear>
        <angular>0</angular>
      </velocity_decay>
    </link>
    <joint name='Castor_F' type='revolute'>
      <child>Castor_F</child>
      <parent>Base_plate</parent>
      <axis>
        <xyz>-3.34991e-06 1 -1.50683e-06</xyz>
        <limit>
          <lower>-1e+16</lower>
          <upper>1e+16</upper>
        </limit>
        <dynamics/>
      </axis>
    </joint>
    <link name='Castor_R'>
      <pose>-0.34387 0.39256 -0.86909 1.5708 -0.93144 -3.14159</pose>
      <inertial>
        <pose>-1.1102e-16 0 0.031164 0 -0 0</pose>
        <mass>0.056555</mass>
        <inertia>
          <ixx>2.4476e-05</ixx>
          <ixy>0</ixy>
          <ixz>-3.9352e-20</ixz>
          <iyy>2.4476e-05</iyy>
          <iyz>-1.951e-20</iyz>
          <izz>7.4341e-06</izz>
        </inertia>
      </inertial>
      <collision name='Castor_R_collision'>
        <pose>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://JMbot1/meshes/Castor_R.STL</uri>
          </mesh>
        </geometry>
      </collision>
      <visual name='Castor_R_visual'>
        <pose>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://JMbot1/meshes/Castor_R.STL</uri>
          </mesh>
        </geometry>
      </visual>
      <velocity_decay>
        <linear>0</linear>
        <angular>0</angular>
      </velocity_decay>
    </link>
    <joint name='Castor_R' type='revolute'>
      <child>Castor_R</child>
      <parent>Base_plate</parent>
      <axis>
        <xyz>-1.02941e-05 1 -2.19172e-06</xyz>
        <limit>
          <lower>-1e+16</lower>
          <upper>1e+16</upper>
        </limit>
        <dynamics/>
      </axis>
    </joint>
    <link name='Wheel_L'>
      <pose>-0.46668 0.40756 -0.70859 2.512 0.081268 3.42872e-15</pose>
      <inertial>
        <pose>-0.039049 2.2204e-16 2.498e-15 0 -0 0</pose>
        <mass>0.45064</mass>
        <inertia>
          <ixx>0.00091608</ixx>
          <ixy>-9.6693e-19</ixy>
          <ixz ...