Originally Posted by kovidgoyal
Ah, now I see it, if you're using --add-simple-plugin then you pass it the path to the .py file not the zip file (the idea is that it makes it easy to add plugins that have only a single py file)
If you want to add the zip file use
calibre-customize --add path to zip file
I went through this morning and re-installed notepad++ and everything seems to be working again.