What version of Mrt software did you use for that ? 184.108.40.206 or 220.127.116.11?
Because on 2.0.x.x software I was having the same problem but on 2.1.x.x it looks like they corrected the reading problem. Now you can read a Samsung Rom, even on M8 series, but don't get excited
, to write a Rom is still not possible. At least not by terminal (that's what I try it ). I don't know about ATA.