have you gone to focusrite and downloaded the drivers for your audio interface ?
if not you need to rid your computer of the substiute windows put in its place and download the right driver.
it could be a buffer issue.if your buffers are to high/low it can make playback unstable.
plug in your focusrite,go to device manager,delete the driver,unplug the unit.re-boot (do not plug it back in)
get the updated driver from focusrite/install it.plug in your unit.
wait for it to accept the driver and open up sonar,you should be running that A.I. with asio only,not anything else.
i have the same unit the saffire 6 usb ?
works great.