oem firmware doesn't matter when using crossflash patched firmware.
nvidia ide drivers or faulty aspi/system files can cause this message.
uninstall the nvidia drivers, if you have them installed, and reboot your pc.
if you don't have these drivers, remove aspi with killaspi.
btw: CG5J is newer, flash with "832S.CG5J.patched-cf-sonyid.exe included in the archive.