Question: I have a USB live key created with Linux Live USB creator. I used all the defaults, and got a standard version of Ubuntu. When I try to boot into it, I get the error above. I went through the rest of the threads with no avail.

Things I tried:

* Renaming the files (my files were already syslinux.cfg, etc.)
* Typing in `mboot.c32 -c boot.cfg` into the boot:\_\_ prompt

Any help would be appreciated!

Answer: 
I've been having the exact same problem. I tried to make USB Live with YUMI and Unebootin with the same error mistake:

SYSLINUX: No DEFAULT or UI configuration directive found!

I've tried to

1. change isolinux etc to syslinux (by copy paste, so there's no spelling mistake)
2. format USB to FAT16 instead of FAT32
3. format USB to FAT16 instead of FAT32 and renaming those files (copy paste)

all failed.

Then I tried to use [Universal USB Creator](http://www.pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/) (same as YUMI but Windows version), and it works!

Just giving alternative suggestions if all you tried failed!
A corrupted download caused this issue for me. Rather download using the provided torrents at <http://www.ubuntu.com/download/alternative-downloads>