i think i know the solution to this. the prob is, you're connecting the novation into different ports each time i bet, so the driver keeps switching from one port to another etc etc.

choose a port you're always going to plug it in (and nothing else) and stick to it. it must always be plugged in when the comp is switched on or the comp will see nothing on the port and the driver will be disassociated with it.

hope this helps