There are several helpful threads to help you understand how installing Plugins work - try this one http://sketchucation.com/resources/tutorials/37-beginner/108-installing-sketchup-plugins Please reread the Fredo's tool's/Lib download page and ensure that you are correctly making the footprint of the files/subfolders-of-files. You do NOT 'install' the folders formed by the UN-zipping process [which are usually named after the ZIP itself and are a temporary resting place for the contents, before you more everything 'intact' into the Plugins folder]... If you diverge from this it can break SketchUp... If you already have please tidy up the misplaced files etc first... I also see you are on a MAC... so please check you are using the correct 'plugins' folder ['HD' path NOT 'user']