no monobehavior scripts in file?

I’m trying this Unity tutorial for a platformer and for whatever reason I keep getting this error “No monobehavior scripts in the file, or their names do not match the file name”. What does this mean?

For reference: The tutorial is here Mini-Projects from the Recorded Video Training Archive - Unity Learn

The script I’m having trouble with is the SimplePlatformController script. I’m certain there are no errors, as I’ve made sure to follow exactly what the guy has said.

You need to check the name of your file matches the name of class. Like this.

Thanks a lot.