Not having loaded sketchup.rb first must have been the problem. When I restored my plugins, I loaded all fo the my_programs first, the first of which did not load sketchup.rb. Once bezier.rb loaded before my_programs, since it loads sketchup.rb, there was no error when my_program loaded.
Any idea what caused my animation to export after removing the plugins, and why it continues to export after replacing all the same plugins?