Failed to load joint?_*_controller

edit

Hello, I have ROS Hydro on Ubuntu 12.04.4.

I have made

$ sudo apt-get install ros-hydro-desktop-full
$ sudo apt-get install ros-hydro-gazebo-ros-pkgs ros-hydro-gazebo-ros-control

and I have downloaded the gazebo_ros_demos into my

catkin_ws/src

I want to try http://gazebosim.org/tutorials/?tut=r... .

Until I type

   $ roslaunch rrbot_gazebo rrbot_world.launch

everything is fine.

But then, when I type

   $ roslaunch rrbot_control rrbot_control.launch

then it says

[ERROR] [WallTime: 1403516339.376075] [33.377000] Failed to load joint_state_controller
[ERROR] [WallTime: 1403516340.379782] [34.378000] Failed to load joint1_position_controller
[ERROR] [WallTime: 1403516341.383720] [35.379000] Failed to load joint2_position_controller

What have I made wrong? What can I do, so that it works?