Hi Knurek, I tried that as well, both GENH and genh in case of case-specific code. Unless I understand your .bat file wrong - mine does:
for i in 1 2 3 4 5 6 7 8 9
	cat IniD_0$i.GENH IniD_0$i.spsd > IniD0$i.spsd.new
	mv IniD0$i.spsd.new IniD0$i.spsd
Since there was no output file specified in your "copy /b ...GENH + ...SPSD" I tried both ways, but vgmstream isn't happy. I wish it would give a better error message (at least I code grep a return code in the source) shocked