Similar to my Mark XI control. I think you will find that there are several versions of the system disk and they must be matched to the proper version of the EPROM chips that are in your control board. You will probably have to find someone with the exact same version as you or at least has the same EPROM chips. Otherwise you might have to call Sodick to get one.
Also the 720KB disk drives in the Japanese NEC computers fail sometimes and they are hard to get hold of as they are special. You might want to put your system disk in a regular desktop PC (Windows XP or older) and see if it is readable. There might be nothing wrong with it.
Once you get your problem resolved, It is a good idea to get a bitwise image of your system disk as they fail frequently and are finicky. I use a program called DiskFactory to create new system disks from my saved image for my Sodick.