I have the exact same problem with freezes. It used to be worse before the last firmware upgrade (have had my cybook for 6 mths or more) so I had assumed that it was firmware related and was hoping the next release (when!!!) fixes it permanently.
I get the problem without use of an SD card and I always eject the device correctly.
Post back on your progress with this taspool. very interested to know if you manage to solve the problem.