If you're updating a script, you might have, by accident, posted the script's contents into the wrong section. When I've done that, during a hasty edit, I've seen very cryptic errors.
See if you can see your script contents in any other one of the scripts in the list. If you pasted it into, say, the Game_System line by mistake, you'll need to create a fresh project, and copy the Game_System line from that into your current project to fix it.