Just checking:
S5020.zip 643.970 bytes
S50V20.out 743.729 bytes

I've downloaded the files from Roland site and tested on my computer, works fine.
Note that Sdisk.exe is a DOS program; it will work under Win 9x, but the disks are not written correctly. If you use Windows, quit to DOS mode and use the program.
The file S50V20.out is a 720k floppy image, it will not work with high density floppies.

Please let me know if sdisk worked for you.

Mgomes