Thwarted in attempt to install fvdw-sl-console

Hello
I have an NS2 which I've been using solely as a file-serving NAS, running laCie's native firmware (currently 2.2.8.4). I've been dithering over whether to install the fvdw-sl-console on it and with that in mind I downloaded ver. 14 in readiness - however didn't go further with it at that time. Now I've decided to go ahead, and have therefore today downloaded (latest) update fvdw-sl-15-3 But I now find myself completely stymied!
When (last November) I downloaded update 14 there was only one (.rar) file to download which I was able to unpack without any problem, and the 16 objects it contained included fvdw-sl-console.exe The download for update 15 has as you know 3 such files - named as parts 1, 2 & 3 - which have to be individually downloaded (I presume - at least, that's what I did). Unpacking these in order, when I reach part 2 I'm asked if I want to over-write the .bin file that was the only file in part 1; if I reply 'no' the unpacking aborts, if I reply 'yes' 7zip brings up an error-message "Data error in 'xfvdw-s1-15-3-nwsp2-30may2014.bin'. File is broken" - and still aborts!
Doubtless I'm missing some essential step that's obvious to everyone else and is probably staring me in the face, but to my inexperienced eye this behaviour is totally inexplicable. I would be most grateful if somebody could please explain to me what it is I have to do that I've failed to do?
Edit
I ought to have mentioned that I'm running Windows 8.1
I have an NS2 which I've been using solely as a file-serving NAS, running laCie's native firmware (currently 2.2.8.4). I've been dithering over whether to install the fvdw-sl-console on it and with that in mind I downloaded ver. 14 in readiness - however didn't go further with it at that time. Now I've decided to go ahead, and have therefore today downloaded (latest) update fvdw-sl-15-3 But I now find myself completely stymied!
When (last November) I downloaded update 14 there was only one (.rar) file to download which I was able to unpack without any problem, and the 16 objects it contained included fvdw-sl-console.exe The download for update 15 has as you know 3 such files - named as parts 1, 2 & 3 - which have to be individually downloaded (I presume - at least, that's what I did). Unpacking these in order, when I reach part 2 I'm asked if I want to over-write the .bin file that was the only file in part 1; if I reply 'no' the unpacking aborts, if I reply 'yes' 7zip brings up an error-message "Data error in 'xfvdw-s1-15-3-nwsp2-30may2014.bin'. File is broken" - and still aborts!
Doubtless I'm missing some essential step that's obvious to everyone else and is probably staring me in the face, but to my inexperienced eye this behaviour is totally inexplicable. I would be most grateful if somebody could please explain to me what it is I have to do that I've failed to do?
Edit
I ought to have mentioned that I'm running Windows 8.1