[Moto E Q&A, Help & Troubleshooting] thangeram:
C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot oem lock

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

...

(bootloader) WARNING: This command erases all user data.

(bootloader) Please re-run this command to continue.

OKAY [ 0.010s]

finished. total time: 0.010s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot oem lock

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

...

(bootloader) Flash valid Android images now

(bootloader) Then re-run this command to lock

OKAY [ 0.013s]

finished. total time: 0.013s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash logo logo.bin

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:logo: not found

target reported max download size of 536870912 bytes

sending 'logo' (2192 KB)...

OKAY [ 0.071s]

writing 'logo'...

OKAY [ 0.104s]

finished. total time: 0.178s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash boot boot.img

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:boot: not found

target reported max download size of 536870912 bytes

sending 'boot' (16384 KB)...

OKAY [ 0.522s]

writing 'boot'...

(bootloader) Security version downgrade

(bootloader) Image boot failed validation

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 0.710s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash oem oem.img

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:oem: not found

target reported max download size of 536870912 bytes

sending 'oem' (327830 KB)...

OKAY [ 10.228s]

writing 'oem'...

(bootloader) Security version downgrade

(bootloader) Image o failed validation

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 22.612s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.0

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

target reported max download size of 536870912 bytes

sending 'system' (524260 KB)...

OKAY [ 21.521s]

writing 'system'...

(bootloader) Security version downgrade

(bootloader) Image s failed validation

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 21.638s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.1

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

target reported max download size of 536870912 bytes

sending 'system' (522314 KB)...

OKAY [ 21.167s]

writing 'system'...

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 21.191s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.2

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

target reported max download size of 536870912 bytes

sending 'system' (522269 KB)...

OKAY [ 23.148s]

writing 'system'...

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 23.194s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.3

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

target reported max download size of 536870912 bytes

sending 'system' (524204 KB)...

OKAY [ 21.778s]

writing 'system'...

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 21.800s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.4

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

target reported max download size of 536870912 bytes

sending 'system' (524139 KB)...

OKAY [ 24.183s]

writing 'system'...

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 24.235s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.5

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

target reported max download size of 536870912 bytes

sending 'system' (435100 KB)...

OKAY [ 19.291s]

writing 'system'...

(bootloader) Invalid signed image

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 19.320s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash system system.img

_sparsechunk.6

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:system: not found

error: cannot load 'system.img_sparsechunk.6': No such file or directory

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot flash boot boot.img

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

(bootloader) has-slot:boot: not found

target reported max download size of 536870912 bytes

sending 'boot' (16384 KB)...

OKAY [ 0.507s]

writing 'boot'...

(bootloader) Security version downgrade

(bootloader) Image boot failed validation

(bootloader) Preflash validation failed

FAILED (remote failure)

finished. total time: 0.695s

C:\Program Files (x86)\Minimal ADB and Fastboot>fastboot oem lock

(bootloader) slot-count: not found

(bootloader) slot-suffixes: not found

(bootloader) slot-suffixes: not found

...

(bootloader) Still require signed boot.img

OKAY [ 0.006s]

finished. total time: 0.007s

tried both rom dec and feb update with latest adb and moto device manager but bad luck