YUMI: Booting find /menu.lst, /boot/grub/menu.lst, /grub/menu.lst

I'm using YUMI to set up a multiboot USB drive. I'm trying YUMI’s option to Try an Unlisted ISO from the bottom of its selection list, and the ISO files gets copied correctly to the USB drive. The problem is that during the boot when I choose the ISO files to boot from, it's not working.

It's giving me this message: Booting find /menu.lst, /boot/grub/menu.lst, /grub/menu.lst, and nothing happens.