i had this exact problem. it turns out that in my case a "hard reset" solved the issue.
what you will not know unless you go to the sony help website (or read this little pearl) is that just pushing the reset doesn't do much. you also have to press the "page back" and "volume up" buttons at the same time when the screen displays "opening book," then confirm that you want to reset. do the hard reset when you are not connected by the usb cord. this erases everything you've done in the reader but does not affect your library on whatever computer you have the software on so you are not really losing anything except maybe some drawings you've made on the reader.
hope this helps!