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When I hit 'play' or 'record' on Transport the following error message in Protools: Pro Tools could not initialize the Focusrite USB 2.0 Audio Driver.

I had the same issue with my Scarlett 6i6. I got a tip from the guys at Focusrite and now mine works. Possibly it could work for you as well...

I'm on a swedish system so I may not use the correct terms...

What I had to do is deactivate playback and recording in windows for my Scarlett. Rightclick the speaker icon down to the right on the systembar of windows. Choose "playback units". Rightclick your Scarlett and deactivate. Do this for both playback and recording. Then start PT.

IF you have changed to a session with a different bitrate than you just used the problem will reoccur and you have to open the session and restart PT (reopening the session) before you try to play anything.

Could be wort a test at least...