1. Mac OS sometimes puts hidden files on SD cards related to Spotlight search, which can confuse Zoia on boot up.
2. Plug SD card into your Mac and use Command + Shift + . (period) to see the hidden files. Move them to trash, unmount the drive, and voila! It should work fine going forward. 
3. If you plug the SD card back into your Mac and the issue recurs, follow steps 1-2 again.