On Fri, May 3, 2013 at 5:14 PM, Fons Adriaensen <fons@linuxaudio.org> wrote:

The second one is an Ardour2 session that worked perfectly
on another similar PC, but becomes completely unresponsive
on the one to be used. It has four mono tracks and three
10-channel ones, and little else. DSP load is not the problem,
it's less than 15%. Things look like it's the graphics.

This follows reports we've seen on IRC many/several times, with no particular combination of video h/w and drivers identified.