nexus 4 : fastboot error downgrading from lollipop to kitkati topic

following is the message coming... please help.


c:\adb>flash-all.bat
...
FAILED (remote: Already Unlocked)
finished. total time: 0.001s
erasing 'boot'...
OKAY [ 0.006s]
finished. total time: 0.006s
******** Did you mean to fastboot format this parti
erasing 'cache'...
OKAY [ 0.019s]
finished. total time: 0.019s
erasing 'recovery'...
OKAY [ 0.005s]
finished. total time: 0.005s
******** Did you mean to fastboot format this parti
erasing 'system'...
OKAY [ 0.032s]
finished. total time: 0.032s
******** Did you mean to fastboot format this parti
erasing 'userdata'...
OKAY [ 0.453s]
finished. total time: 0.453s
sending 'bootloader' (2100 KB)...
OKAY [ 0.082s]
writing 'bootloader'...
FAILED (remote: invalid bootloader image
)
finished. total time: 0.084s
rebooting into bootloader...
OKAY [ 0.001s]
finished. total time: 0.001s
sending 'radio' (16384 KB)...
OKAY [ 0.540s]
writing 'radio'...
OKAY [ 0.880s]
finished. total time: 1.422s
rebooting into bootloader...
OKAY [ 0.001s]
finished. total time: 0.001s
archive does not contain 'boot.sig'
archive does not contain 'recovery.sig'
archive does not contain 'system.sig'
--------------------------------------------
Bootloader Version...: MAKOZ30f
Baseband Version.....: N/A
Serial Number........: 05ed6845a00e183c
--------------------------------------------
checking product...
FAILED

Device product is 'mako'.
Update requires 'tilapia'.

finished. total time: 0.012s
Press any key to exit...