Luis, I figured it out. It was a 3rd party plugin that wasn’t compatible with Motion 5.4.6. Create a new finder window and go to Motion Templates. Create a new folder called TEMP PLUGINS and drag it to a new finder window. Move all Plugins from the COMPOSITION FOLDER, GENERATORS FOLDER, TITLES FOLDER, TRANSITIONS FOLDER into the TEMP folder. LEAVE THE EMPTY COMP, GENERATOR, TITLES, TRANSITION folders in Motion. Restart Motion 5 and it should open now. Then you can slowly drag the plugins back into Motion from the TEMP folder to see which plugin is causing the issue. Depending on how many plugins you have it may take some time. Give it a try and let me know. It worked for me.