Sorry I'm a new user but I'm having trouble with two Retroarch cores. The mednafenpsx core issue has been reported but I'm also seeing a similar failure to launch with parallel_n64_libretro.dll. I noticed the Runway app is listing the old file name for this core 'parallellibretro' but it was updated sometime last March 2019 (or earlier) to use the new name. I tried renaming the core with the old filename but that didn't help it launch.