[bazza]

Are you selecting Internal Storage or SD card as the destination? Please select SD Card if you are not currently.

Thanks for the reply: the problem seems to be that the sdcard (i.e. the 'internal' one) is shown as 'empty, unmounted or not present'. I've looked for it using es Explorer but it doesn't seem to be there, and if I use Terminal Emulator it refers to is but shows 'permission denied'. It's apparently a brick wall scenario.

I do find it confusing that the 'sdcard' route I need seems to be an internal storage facility, but separate from 'Internal Storage' and not actually an SD Card as usually understood (i.e. externally inserted).

If you could tell me how to select it, as you suggest. . . . Otherwise is the only recourse is to go for a factory reset? As I'm new to this game, I could be missing something obvious, so advice welcome!