No transform from links to odom in rviz

I built an URDF model from scratch and launched successfully in gazebo. Then i added the differential_drive and joint_state plug-ins to the urdf model as followsWheel_LWheel_Rbase_plate0.2350.12trueCastor_F, Castor_R Finally i launched the model in Gazebo and when visualized in rviz, there comes the error "no transform from [links] to [odom]" ref the image below  The bizarre is the error doesn't occur when the fixed frame is set to any links. I have launched the empty world and spawned the robot in it. I have also launched robot_state_publisher and below is my launch file