SOLUTION:
I know this is an old topic, but I had the same problem and the solution was to try a different USB drive. It might be the firmware on the USB or something that is conflicting with the Control4 creator. But I tried a 16GB thumb drive and it worked for me.
Also, to get around the lock issue; just open up my computer, right click on the drive and format the USB. This will unlock it from any system utility using it. Then try again with the Control4 creator.