Flashing rootfs in fastboot mode for wp8 is not working

I am using WP8 mango OH development board. Compilation environment beta 15.05.
When i recompiled my rootfs with additional recipe added. i cannot flash the rootfs using fastboot mode.

command used
fastboot erase rootfs
fastboot flash rootfs rootfs
… failed

Note: I can able to flash the same in WP7
I have pointed the image to 2k image.

Topic moved to the correct section.