n920i odin failing

Not that familiar with odin or samsung, previously htc :)
using odin in a windows 7 virtual machine under ubuntu, if that makes a difference
Trying to flash australian optus firmware over singapore firmware my phone came with but odin fails iafter initilization so not sure where to go next
really want australian settings and keyboard etc
Cant upload a screencapture sadly but odin fails after the setupConnection step
and returns complete (write) operation failed?
using latest drivers etc? Anyone got an idea of what im doing wrong?
Do i need to activate something in developer options or something to allow odin to connect?

Update failing after unrooting

I had my S6 root with pingpong, but I had to unroot to use Ariwatch MDM agent for my work. I unrooted by going into Supersu and doing "full unroot". But now when I try to install the update OE2 it fails. I;m looking to install 5.1.1 update eventually.

Any thoughts?

thanks