This thread should help:
https://www.mobileread.com/forums/sh...d.php?t=278728
Summary: You can either try to hack your PB to get it working with a new SD card following the above mentioned thread or contact the Russian Pocketpook service <service@pocketbook-int.ru>, which will probably help you to get a new image for a card you can buy yourself. I did it and they did this service for affordable about 6 USD.