Ok guys, I have a problem.
I managed to downgrade to 5.4.5.1 using the diags mode and following all the instructions here. (I followed ALL and it worked, that's not the problem)
Now, since I also got the error message ''Your Kindle is no longer a test Kindle and is unable to test items previously signed by authorized developers. If you want your device to be a test Kindle again, please contact the developer.''
when I tried to open KUAL (same as the original poster), moreover, I couldn't reinstall the original 5.6.5 jailbreak because it gave me an error at Step 2 (it has closed the Experimental Browser by itself), I tried to just install the bridge to get back the jailbreak:
update_jailbreak_bridge_1.7.N_install.bin
which I installed, and now tried to reboot my Kindle but it only opens in diags mode and I dont know how to exit it. Even if I click X) Exit , it doesnt want to exit...
How can I get back my normal working jailbroken Kindle and quit this stupid diags mode?