[NiLuJe]

That post wasn't really directed at cases like this, the U007 error is pretty straightforward: failure to check the package signature, which usually means the device is not jailbroken.

To recap, make sure you don't have another jailbreak installed/half installed, and reboot your kindle before installing new stuff if you manage to get a jb uninstall to finish succesfully.

Also, the folder is not a good thing to check for success, it will never be deleted automatically, even during a successful uninstall, the only trustworthy indicator is the return status/code of the updater :-) .

You should be able to 'revive' the usbnet hack after a factory reset the same way as the jailbreak: just put the usbnet folder from the packages back on the root of your userstore. You probably will need to do a reboot to get the private usbnetwork command working, or you could try using the auto mode, if you're confident in your setup (mainly, don't enable ssh over wireless).

If you manage to get a shell access back, check the state of the update private keys, the logs, and if any of the partitions are nearly full.