Worked out why the texture backup failed....Service pack 2 must be installed for the ASE2012 backup function to work fully without the error message.
The texture files missing are not added until SP2 is installed.....this is annoying as the product page for ASE2012 states it is compatible with FSX with either SP1 or SP2.
I dont want to install SP2 as it 'breaks' the vsync in the game and gives a distorted wave/ripple which is impossible to lock down with AMD card and drivers.
I realise that ASE will technically work with SP1 but i would be nervous about installing new textures when i dont have a full backup.
Does anybody know if REX is okay with just SP1 installed?