Error [Plugin.hh:138] Failed to load plugin libgazebo_ros_camera.so: libCameraPlugin.so: cannot open shared object file: No such file or directory

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Hello guys, I have the following issue on gazebo 1.9 (ROS Hydro - Ubuntu 12.04): I have a package, for example pioneer3at, where in .sdf file some plugin, as libgazebo_ros_camera.so, are inserted. When I type roslaunch pioneer3at myfile.launch

it gives me this error

Msg Waiting for masterMsg Connected to gazebo master @ http://127.0.0.1:11345
Msg Publicized address: 172.20.242.19
Error [Plugin.hh:138] Failed to load plugin libgazebo_ros_camera.so: libCameraPlugin.so: cannot open shared object file: No such file or directory

I tried also to set env variable GAZEBO_PLUGIN_PATH correctly but however it doesn't work. However I noted that, in a tutorial of gazebo about RRBot Example, when I typed roslaunch command, it gave me the same error but with a several plugin:

Error [Plugin.hh:138] Failed to load plugin libgazebo_ros_control.so:libgazebo_ros_control.so: cannot open shared object file: No such file or directory

To resolve this last problem, I installed ros-hydro-gazebo-ros-control package. Now my question is: to resolve the problem with libgazebo_ros_camera.so:libCameraPlugin.so, I should install a missing package or what? This is really important for me... Excuse me and thanks to all