I am having the same problem. Spotty was working ok yesterday, today i get the same error message when I’ve loaded a playlist; Problem: can’t open file for: then the name of the file.
I’m using the Spotify family plugin which works, however you have to rebuild your playlists and artist lists as these don’t port over onto this plugin. It’s based on the Triode plugin, which I couldn’t find. To use it add this link to the repo list in the settings, plugins page of LMS: