Try a different USB stick, format it to FAT 32, using your PC, before loading the vuplus folder onto it.
Are you following the guides, on how to update?
Power Off your VU+ Solo2, using the power switch, at the rear
Insert USB Pen Drive in the front USB socket.
Power on the VU+ Solo2, using the power switch, at the rear.
When prompted to update, press the Blue Circle (Power On) button on the front of the receiver.
Once the image has installed the receiver will automatically reboot.