I deleted an stl file while pathio was down. It was the file that it currently had on the build plate. When I started pathio subsequent to this, I got a message that the file could not be loaded, and the circular icon indicating that it was working kept spinning. I could load additional files, but the slice button was disabled so I couldn’t slice anything.
I had to exit the program and manually edit the startup file to remove the reference to the nonexistant file.