There is a known issue with the current software where Misty returns an error when you try to upload a the .zip file for a skill that was created on a Mac. Additionally, Misty becomes unable to load or start skills after the failed upload attempt.
This issue will be addressed in a forthcoming update to Misty's system. For now, if you are a Mac user, you can still upload skills to Misty by creating a .zip for your skill using one of the options below.
Note: If you already tried uploading a .zip compressed on your Mac, you need to restart Misty before either of these options will work.
Option 1: Use an online file compression tool to compress your skill files into a .zip folder.
Option 2: Use the terminal to create the .zip and prevent additional files from being created in the compressed folder.