@LindzB said in Fatal error occurred: fatal error occurred: Could not open COM3, the port is busy or doesn't exist. (could not open port 'COM3': PermissionError(13, 'Access is denied.', None, 5)) Please, I need help in correcting this error. Are you using M5Burner? is com3 detected in it for your device? is there diff software with your com port 3 opened in it in the background? lack of info about your hardware/software setup really