Thank you for your reply, uboot. Actually at the moment, my Reader is not rooted so fixing permissions and all the rest is not a real option.
Actually I tried rooting it again and the rooting failed. It never got out of recovery mode after a much longer time that usual and a manual reset blocked my Reader. So I reflashed the restore set. I got a working reader again even though the "script" file contained gibberish.
In one of your links I read about a Ramdisk. From what I know, this is a temporary disk created in RAM to store the kernel, right? In which partition is the kernel installed? Is there a way to check for it's integrity?