I've noticed that a lot of people have asked this before, but no method that I've found seemed to work, so I apologize in advance.
I've created a custom Live USB using the Ubuntu Customization Kit and a stock image of Ubuntu Desktop 14.04 64-bit. The reason for creating the custom image is because I would like a lot of the tools that I use regularly (Qt, ADT, build-essential, etc) to already be available instead of having to download 1GB+ every time I'm somewhere without my regular machine.
I'm using YUMI 220.127.116.11 to create by bootable USB flash drive, which works great for the stock image.
Whenever I try to load ANY customized ISO via USB generated by UCK, it gives the error message:
(initramfs) unable to find a medium containing a live file system
However, when I burn the ISO to a DVD, it boots without a problem.
I've edited the isolinux.cfg to put 'vmlinuz.efi' at the end of live-media-path, thinking that might be it. I've tried to find information about where Ubuntu looks for the UUID of the device, only found it in the 'casper-uuid-generic' file.
Anyone have any ideas? Thanks for any help!