Problem launching a plugin [closed]

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Hello, I'm trying to launch a gazebo plugin following all the instructions on: http://www.ros.org/wiki/simulator_gazebo/Tutorials/GazeboPluginIntro but on the bash this error appears:

Error [Plugin.hh:100] Failed to load plugin libanimate_joints.so: libanimate_joints.so: cannot open shared object file: No such file or directory

But I'm not able to find a sense..... Thanks