[Nexus 6 Q&A, Help & Troubleshooting] gareth321:
I had my nexus 6 rooted and unlocked then wanted to unroot to be able to upsdate to M.

Although when I tried to re-flash it ended up not being able to boot back up. now i have a nexus in bootloader but cannot get the system.img to flash.

I have tried doing all indiviually as well as using the flash all.bat . and i get this error everytime

sending sparse 'system' (522932 KB)...

FAILED (data transfer failure (Unknown error))

I have also tried using twrp to move over the .zip of the factory 5.1.1 and it just stops transferring about a 3rd of the way through.

I am fairly certain that i have the latest fastboot as well as all the latest from the sdk tools manager

< waiting for device >

target reported max download size of 536870912 bytes

sending 'bootloader' (3807 KB)...

OKAY [ 0.133s]

writing 'bootloader'...

(bootloader) flashing partition ...

(bootloader) This may take a few seconds if a

(bootloader) different partition table is being

(bootloader) flashed since we need to backup

(bootloader) and restore a few partitions

(bootloader) Flashing primary GPT image...

(bootloader) Flashing backup GPT image...

(bootloader) flashing aboot ...

(bootloader) flashing sbl1 ...

(bootloader) flashing rpm ...

(bootloader) flashing tz ...

(bootloader) flashing sdi ...

(bootloader) flashing logo ...

OKAY [ 0.363s]

finished. total time: 0.497s

rebooting into bootloader...

OKAY [ 0.003s]

finished. total time: 0.004s

target reported max download size of 536870912 bytes

sending 'radio' (85419 KB)...

OKAY [ 2.790s]

writing 'radio'...

(bootloader) flashing modem ...

(bootloader) flashing mdm1m9kefs1 ...

(bootloader) flashing mdm1m9kefs2 ...

(bootloader) flashing mdm1m9kefs3 ...

(bootloader) flashing versions ...

OKAY [ 1.142s]

finished. total time: 3.932s

rebooting into bootloader...

OKAY [ 0.000s]

finished. total time: 0.000s

target reported max download size of 536870912 bytes

archive does not contain 'boot.sig'

archive does not contain 'recovery.sig'

archive does not contain 'system.sig'

archive does not contain 'vendor.img'

Creating filesystem with parameters:

Size: 28474998784

Block size: 4096

Blocks per group: 32768

Inodes per group: 8160

Inode size: 256

Journal blocks: 32768

Label:

Blocks: 6951904

Block groups: 213

Reserved block group size: 1024

Created filesystem with 11/1738080 inodes and 153124/6951904 blocks

Creating filesystem with parameters:

Size: 268435456

Block size: 4096

Blocks per group: 32768

Inodes per group: 8192

Inode size: 256

Journal blocks: 1024

Label:

Blocks: 65536

Block groups: 2

Reserved block group size: 15

Created filesystem with 11/16384 inodes and 2089/65536 blocks

--------------------------------------------

Bootloader Version...: moto-apq8084-71.10

Baseband Version.....: D4.0-9625-02.101

Serial Number........: ZX1G22CVC4

--------------------------------------------

checking product...

OKAY [ 0.002s]

checking version-bootloader...

OKAY [ 0.003s]

checking version-baseband...

OKAY [ 0.003s]

sending 'boot' (7741 KB)...

OKAY [ 0.250s]

writing 'boot'...

OKAY [ 0.109s]

sending 'recovery' (8331 KB)...

OKAY [ 0.297s]

writing 'recovery'...

OKAY [ 0.125s]

sending sparse 'system' (522932 KB)...

FAILED (data transfer failure (Unknown error))

finished. total time: 21.199s

Press any key to exit...