No reader handles all the ebook formats that are out there.
Assuming that you understand the above, and that you bought the Jetbook for reading
the formats that it says that it can read, which formats (that it claims to be able to
read) are you having problems with?
What file structure are you using for your eBook library? Have you read the threads
here that address the "Hourglass of death" issue?
Why do you think going from the current stable firmware 0.33g, offered at the Ectaco
site for the JB, to a version that they are not offering; would correct whatever problems
you are currently having?
Luck;
Ken
P.S. Perhaps this :
https://www.mobileread.com/forums/sho...7&postcount=15