error unlock bootloader

Hello
I try to unlock the bootloader of my zuk Z2 pro but I am having a problem on the last command following this : http://ift.tt/2d3Wr84

C:\Windows\system32>C:\adb\fastboot -i 0x2b4c flash unlock unlock_bootloader.img
error: cannot load 'unlock_bootloader.img'

the file is at the root of fastboot and adb



Thank you for your help

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