You may want to mount the MMC on a Linux system and write 0s to the initial few blocks.
Find the device using lsblk, then run dd if=/dev/zero of=/path/to/device (/dev/sd??) bs=1M count=16. Then try again in disk part
Find the device using lsblk, then run dd if=/dev/zero of=/path/to/device (/dev/sd??) bs=1M count=16. Then try again in disk part