Korg PA 600 unable to upgrade OS

[kgopu24]

I bought this korg pa 600 in 2015, I have been using the OS 1.2 2014 version, but now I am unable to update to 1.2 2018 version, Once I press intro button and power button,, I get system update msg but then it doesnt proceed to calibirate page for me to proceed further, instead it just hangs at the same page.
When I try factory restore from media utility, I get a msg stating back up file is damaged hence restore is interrupted.
Kindly tell me how to remove the damaged back up file.

K GOPU.
kgopu24@gmail.com