The problem could be your SD card inside your Kobo needs replacing with a new one. You can Go this this thread and request a new firmware image to be able to write to a new SD card.
https://www.mobileread.com/forums/sh...d.php?t=355778
You will also have to go to the thread to request PMs be enabled.
https://www.mobileread.com/forums/sh...d.php?t=319819