Could not load controller 'smart_arm_controller', why?

edit

I have the following parameter on the server:

 /smart_arm/smart_arm_controller/type =
      robot_mechanism_controllers/JointTrajectoryActionController

and in a launch file I do

 node name="controller_spawner" pkg="controller_manager" type="spawner" respawn="false"
        output="screen" ns="/smart_arm" args="smart_arm_controller
                                              shoulder_pan_controller
                                                       ....

then why do I get the following error message:

[ERROR] [1428415830.676479048, 0.952000000]: Could not load controller 'smart_arm_controller' because controller type 'robot_mechanism_controllers/JointTrajectoryActionController' does not exist.

Note that I do have the package robot_mechanism_controllers installed.

I am at a loss here.