Resolving a 'Pro Tools could not initialize the Saffire' Pro 26 issue on Win 8.1

I'm setting up a new PC with Pro Tools 11.3 and Focusrite Saffire Pro 26 interface. I have what I think are the latest drivers from http://global.focusrite.com/download...Saffire+PRO+26. 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 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. Also upgraded to 11.3. Can anybody help advise? I'm new to Pro Tools.