The add-on has been changed, you need to try again with the newer add-on
Try this link to explain, a few scripts have been removed and new ones used, so the launcher is looking for a script that isn’t there anymore or trying to run something it can’t find. It took me a long time to find that out
It explains how to update the RetroSMC script to the latest release and how to install the new launcher. It works fine after that
I have a different issue that things are running really slooow when trying to play ANY games. I know it worked perfectly before when I first found RetroSMC. I even reinstalled OSMC from scratch on a fresh and did everything exactly as the add-on suggests, still runs slow when trying to play ANY games. Overclocked PI3 that works perfectly otherwise running KODI 17.6