Fastboot error while unlocking bootloader of Canvas Nitro

OS: Windows 7
ROM: Android 4.4.2 (stock)
Device: Micromax Canvas Nitro A310 (Indian)
USB cable is fine. MTP mode is flawless. USB debugging mode activated. ADB, Fastboot drivers successfully installed. USB drivers downloaded from xda are installed . To unlock the bootloader I issued the following commands.
adb reboot bootloader //It successfully booted to fastboot mode
fastboot devices //prompt says nothing
fastboot oem unlock //<waiting for device>

Followed the same procedure for my Micromax Canvas A1, which is successful with the same PC.
It's the Nitro that is stuborn.

Thanks for the help