system check-installation result has bad file!

[admin@MikroTik] > system check-installation
damaged system package: bad file /flash/boot/kernel
[admin@MikroTik] >

Hi Guys,
We have RB1000 with firmware latest released. Sometimes it’s not booting. If boot success on lucky there are not any problem in RouterOS.
And we checked

system check-installation

command, the result shows

damaged system package: bad file /flash/boot/kernel

.
We changed RouterBOOT and RouterOS versions and also formatted the nand memory, but not success to resolve the problem.
What would we do?