It sounds like the iso is not loading properly on the USB drive. I've had issues with unetbootin in the past.
If you are using a Linux machine do the following.
1. Use Gparted to format the USB drive and load fat32 file system
2. Use the dd command to load the ISO. example sudo dd bs=4M if=iso-file of=/dev/sbx (sbx is the USB drive don't use sbx1)
If you are on Windows
1. Format the USB drive to fat32
2. Use http://www.pendrivelinux.com/
to copy the ISO to USB