Saffire 6 interface not talking to logic 9 in yosemite

I've been hapilly using the saffire 6 with my iMac for years but for convenience I've also just put Logic 9 on my Macbook (running Yosemite).

My connection between MacBook and Saffire6 seems okay with USB light illuminated and it appears (and is selected) on the preference panels in logic9.

However, no audio is transmitted and from the moment Logic9 launches all one can hear is, what I assume,is fast continuous midi 'ticking' . Approx rate of 2 a second and the midi light flashing on the front of the saffire.

Any help would be much appreciated.

btw, I folowed some of the focusrite support tips and dumped some duplicate 'device & system settings' in library preferences. But no change.