twelve posts prior to yours, in this thread:
https://www.mobileread.com/forums/sho...&postcount=884
You did the first part, now do the second (run the 'hotfix').
The 'hotfix' installs, among other things, the jailbreak 'survival kit', once that is done, the 'bridge' code will re-install the jailbreak and the MKK developer keys after each update to the firmware version.
Note: With firmware series 5.6.x and 5.7.x you **MUST** use KUAL and the MrPI KUAL extension to install any of our update_*.bin packages.
(Both KUAL and MrPI are in stickies)