Error in amcl node while configuring navigation stack simulation

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I have configured the navigation stack to a mobile robot model. When i tried to launch the below file got a following error. I am sure the error is with amcl node because i checked other nodes, launch file works fine without the amcl node.

<launch>
  <!-- Load the TortoiseBot URDF model into the parameter server -->
  <param name="robot_description" textfile="$(find jmbot1_description)/urdf/jmbot1.1.urdf" />
  <!-- Start Gazebo with a world containing a large building-->
  <include file="$(find gazebo_ros)/launch/willowgarage_world.launch"/>
  <!-- include file="$(find gazebo_ros)/launch/empty_world.launch"/ -->
  <!-- Spawn a TortoiseBot in Gazebo, taking the description from the
       parameter server -->
  <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" 
    args="-param robot_description -urdf -model jmbot1.1 -x 8 -y -8" />

<!-- Convert /joint_states messages published by Gazebo to /tf messages,
       e.g., for rviz-->
  <node name="robot_state_publisher" pkg="robot_state_publisher"
        type="robot_state_publisher"/>
  <node name="map_server" pkg="map_server" type="map_server"
        args="$(find mapping)/src/maps/willow.yaml"  />

<include file="$(find amcl)/examples/amcl_diff.launch"/>

  <node pkg="move_base" type="move_base" respawn="false" name="move_base" output="screen">
    <rosparam file="$(find jmbot1_description)/src/costmap_common_params.yaml" command="load" ns="global_costmap" />
    <rosparam file="$(find jmbot1_description)/src/costmap_common_params.yaml" command="load" ns="local_costmap" />
    <rosparam file="$(find jmbot1_description)/src/local_costmap_params.yaml" command="load" />
    <rosparam file="$(find jmbot1_description)/src/global_costmap_params.yaml" command="load" />
    <rosparam file="$(find jmbot1_description)/src/base_local_planner_params.yaml" command="load" />
  </node>


</launch>

Error:

[ERROR] [1454003234.548580927, 485.467000000]: Couldn't transform from hokuyo_link to base_link, even though the message notifier is in use

I have verified the rqt_graph and here is it for ref