[Grml] Creating Live USB with grml2usb

I would like to put grml live cd on usb drive. I created bootable w96 fat32 partition and formatted it using mkfs.vfat. I ran "grml2sub grml.iso /dev/sdb1".

I am getting boot error.

I tried to create live usb with unetbootin. This worked. Would anyone have an idea what is going wrong?

Thanks in advance