I've seen NOT_READY errors after removing and reinserting the SD card. Sometimes. I've also had 2 micro SD cards fail in the past 2 years, despite not using SD cards much; the one that failed while in an Espruino went over to giving NOT_READY errors.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I've seen NOT_READY errors after removing and reinserting the SD card. Sometimes. I've also had 2 micro SD cards fail in the past 2 years, despite not using SD cards much; the one that failed while in an Espruino went over to giving NOT_READY errors.