Hi there,
I've not come across any problems when using USB Sticks but they do seem to occur for a lot of users.
Are you using a PC or MAC to format the USB Drive? USB Sticks that have been formatted on a MAC don't always work on a PC.
Have you tried formatting the USB Stick in NTFS or FAT32? I regularly install Windows OS using a USB Stick but this had to be formatted in NTFS.
What size is the USB Stick? There can sometimes be problems if you use drives over 8GB for BOOTING purposes.