I used Prepros 4.0.1 (WIN) to compile scss files.
Have no problem compiling gumby.scss from the downloaded package (Gumby-master.zip). But when I used Claymate to create my project and try to compile sass\gumby.scss , this error message appears:
RuntimeError on line ["122"] of D: can't modify frozen Array
Run with --trace to see the full backtrace
Seems that the problem occurred because I didn't install Ruby & Compass when typing claymate install and adjust Prepros to use custom Ruby for SASS
So I installed them, configured Prepros to use custom Ruby for SASS and successfully compiled sass\gumby.scss
Awesome, glad you figured it out!
Just chiming in to say thank you so much. This really helped me out!