[ixtab]

I'm only guessing, but it's most probably the indexer having problems with one or more books.

You can get your system log files by entering ";dm" in the search box - they'll be stored somewhere on the USB. You may want to take a look at them and check if there is anything unusual in there.

Of course, you can also install usbnetwork and connect directly to the device, then check things like running processes etc., or monitor the log files in realtime. That requires Linux knowledge though.

Otherwise, you could try a factory reset to see if the problem goes away, and then gradually re-add your books to see if it starts appearing again. The "good" thing about the new FW updates is that they are actually full partition images, so the procedure for uninstalling the jailbreak (see the JB thread) will always give you a "really factory fresh" Kindle.