Struggling to update from 7.3.2 to 7.5.4 "something unexpected happened"

    I bought it second hand and it came reset to factory defaults so was running 7.2.something.


    I managed to get it up to 7.3.2 but every time I try to update to 7.5.4 I get the attached error.


    I'm using a USB stick and I've tried putting the kaos.bin file in both the root and OS Update folder with the same results.


    Should the Rig Manager (3.0.136) app do this update? All it says when it starts is that an update is needed but it might take a few minutes to arrive and nothing seems to happen.


    Any ideas?


    Given it's the weekend I thought I'd try here first rather than emailing support.


    Thanks in advance!