Worked it out.
The Stick was showing V1.13.4, which was the firmware version for UIFlow 1.
I had previously flashed that onto the stick.
When I was burning UIFlow 2, it didn't erase or overwrite the V1 firmware.
I forced an erase by going to Burn / Erase.
The stick is now showing the V2 firmware and I am able to flash new programs to it.