Yeah, it says that it can't "interact" with this back-up memory.
You CAN rescue those Ys IV save files, using a utility called
nanami, which allows you to actually transfer your Duo save files over to your computer, burn it on a CD-ROM, then write it back to your Duo once you format & clear up your system. It's a bit of a pain in the ass because you have to hand-write the binary (or was it hex) code on a sheet of paper (tip: just take digital shots of your TV -- much easier to do than writing it down), then transfer those codes back on your computer by hand-typing them in.