Some USB sticks just refuse to flash, it is that simple. Try and get hold of a bog standard USB stick, no frills, USB 2.0 stick. 2gb, 4gb 8gb. You can use a program called HDguru and low level format your drive, you can re-format to fat32 and you need to check the file structure of the zgemma folder on the stick.
The file structure
——————– sh1 or h3 folder
——————– 5 files
WooshBuild is designed to flash automatically from a USB port in your box. Remove any other devices you have attached or an SD card. With the USB having the zgemma folder on it, turn the box on and it should flash.