@jackieone: U007 (usually) means the JB is not installed.
That should *never* happen on a JB install... except when mixing different JBs.
... and also when uninstalling some buggy JB versions (yifan's included).
I'm unclear if you first successfully ran the uninstall package I attached earlier, but if you did, one quick fix for said buggy uninistallers is to fully reboot the device before trying to install new stuff.
TL;DR: Restart the Kindle and try again (to install the latest JB & ScreenSavers hack)

.