Backing up error topic

I tried to find anyone with a similar issue to no avail so I'm not sure if anyone will be able to help me but basically everything works fine fastboot and adb and according to the root checker I'm fully rooted. But whenever I use

adb shell su -c "dd if=/dev/block/mmcblk0boot0 of=/sdcard/boot0block.img"

or the other backup commands all that comes up is exec: no such file or directory.

Is there something I'm missing or maybe something I overlooked or didnt install properly? Hope it's an easy fix. Thanks in advance.

[Q] Backing up Reader Highlights topic

Hi,

I'm planning to root my Incredible S, but keep the stock ROM.
I use the stock book reader a lot and make a lot of highlights, which I don't want to lose with the other user data when I unlock the bootloader.
Is there any way by which I can backup and restore those highlights? My guess is that they are stored in a database somewhere, but how can I find out? and will I be able to access those files on an unrooted device? Has anyone tried such a thing?

Your help is highly appreciated.