When you insert a USB Stick into a Mac, OS X writes up to four invisible files on the stick. It is these invisible files that make the stick unusable in your embroidery machine. To further aggravate the matter OS X does not know how to format a stick or floppy as MS-DOS FAT correctly. We have talked to Apple about both of these issues.
So what to do?
1. Buy pre-formatted USB Sticks or if you have access to a Windows machine re-format there.
2. Never use OSX MS-DOS FAT formatting. The stick will be unusable in your embroidery machine.
3. Use the File > Save Stitch File As function in Essentials to select a USB stick and save the design. This function removes the hidden files.
4. If you remove the stick after a Save As it should work in your machine.
5. If you re-insert the stick into the Mac and then remove it, it will have hidden files and be unusable in your machine.
6. Use the File > Save Stitch File As feature to remove these hidden files.
We have many videos on our youtube channel, including this one on how to save designs to your USB in the program:
https://www.youtube.com/watch?v=VlGuvT_Oit4&list=PLwm56yBBUPAPIUsI3X7RWyAaFmrP22_5Y