Recuva doesn't recognise my NAS drive

[evilbunny]

I am trying to recover my video files from a USB drive which has stopped working (directory corrupted, apparently). To avoid such loss again, I have decided to replace it with a NAS (Network Accesed Storage) 4Tb RAID1 array (NETGEAR RN10400-100EUS populated with 2x4Tb WD Red drives).
 
However, although the drive is working (I have successfully copied my Music directory over to it, and played an album from it), Recuva doesn't seem to be recognising this drive. I fire up the wizard, and get to the screen asking whether I want to save an image file first. I answer "Yes", and browse to the path for the file as \\READYNAS\Documents\fred.vhd. (I am new to NASes, so I don't know if this is standard behaviour, but a Netgear NAS doesn't allow anything to be saved in the root directory; so anything which is not music, photo or video geos in the catch-all "Docunents" directory.) When I click "OK" from the save dialog to return to the Recuva Wizard, it just sits there; no Next button activation.

 

Does this mean that I will have to borrow a large, empty USB drive (or find some way to connect the NAS as a USB drive) before I can proceed?