Saphire 24 pro won't initialise

I'm setting up a new PC with Pro Tools 11.3 and Focusrite Saffire Pro 24 interface. I have what I think are the latest drivers from http://ift.tt/1Jvm2iY. Saffire MixControl comes up OK and the input responds to the mic. Saffire also appears as selectable in the Pro Tools I/O (e.g. A1) but when I press play or try to record I get a 'Pro Tools could not initialize the Saffire' message. I tried making use sample rates were the same to no affect.
I installed the interface and drivers before installing PT11 and have also re-installed in the same order following a complete system clean and defrag but without any joy.
Any one got any ideas?