I would check the Cool-er disc for errors with the standard Microsoft Windows tools:
- connect the reader to PC via USB,
- open My Computer,
- right-click the Cool-er disk,
- select Properties,
- select Tools,
- press Check Now,
- select "Automatically fix file system errors"
- press Start and wait till the check is done.
If no problems found, I'd try installing firmware of similar devices (e.g., ShineBook - see several links in the "росketbook 301 firmware" thread) to find out if yours are firmware-related problems. It is possible to restore Cool-er firmware afterwards, if you want.
If you decide to try Pocketbook's FW, please remember that there is no way back to Cool-er's.