Problem with spawn_model in gazebo

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Hello,

I am trying to spawn a table and a coffee cup into the empty world of pr2 following this tutorial http://www.ros.org/wiki/pr2_simulator/Tutorials/BasicPR2Controls:

1) I Copied the table.stl to this directory `rospack find   gazebo_worlds`/Media/models/
2) I Copied the table.urdf to this directory `rospack find gazebo_worlds`/objects/
3) roslaunch pr2_gazebo pr2_empty_world.launch----> works fine.
4) rosrun gazebo spawn_model -urdf -file table.urdf -model table -x 1.0 -y 0.5 -z 0.3
5) rosrun gazebo spawn_model -gazebo -file `rospack find gazebo_worlds`/objects/coffee_cup.model -model coffee_cup -x 1.2 -z 1

The result is so weird, the table was spawned with no color(same color as the background) while I have gotten the error message: "filename referred by mesh [table.stl] does not appear to exist."

The coffee cup was shown in the list of models but there is no coffee cup in the world. And there some error messages for this command : "namespace error : Namespace prefix model on physical is not defined"

Why do I get these error messages? And if I delete one object from the world, the entire gazebo window will be closed. Why?

p.s. I am working with Fuerte ROS on Ubuntu 12.0.4

Thanks,