Tried a different one but no joy, same problem.
The only doubt I have is that regardles if I connect the usb key in the top or bottom slot it says dev/sda1
Could that be the problem?
Have you added any other plugin's ?
If so, please reflash your box with fresh image, and format your usb stick again using the usb format wizard, and then mount as /universe.
If that doesn't sort it, you are either missing a step out somewhere (doesn't sound like you are), you have incompatable usb sticks (unlikely) or you have an issue with your box.
Anyhow please try as I suggested, as we had many issue's in testing, but this was not 1 of them, and trust me when I say we did alot of testing with this new feature.