live usb - Failed to run a bootable USB

EDIT: I tried to reinstall syslinux from "Misc Options", and I get an error. mtools crashed using this command: mmove -D o -D O s:/ldlinux.sys s:/yumi/ldlinux.sys.

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This is what I've done until now:

1. attached my USB pen to PC


2. downloaded GParted Live ISO from stable directory


3. installed YUMI for Ubuntu, a program that allows you to create a bootable USB with multiple bootable ISOs


4. run YUMI.gambas from bash and entered my sudoer password


5. selected the USB pen and the ISO, and clicked "Create"


6. Checked that an yumi directory on the pen exists


7. Rebooted PC


8. pressed F8 at BIOS level and selected the pen

Result: USB bootloader was not started. On the contrary, my default bootloader started, and Linux booted. No error message was displayed. Is there a way to debug it?