When I open a session in Ardour then go to Window > Audio/MIDI Setup and change the Device setting, it crashes every time for me.
I was switching between the Generic Low Latency ASIO Driver and the Focusrite USB 2.0 Audio Driver. Switching both directions causes a crash.
If it is helpful, here’s the debug output: http://pastebin.com/KcWHHSCT
Ardour Nightly 64-bit Debug, Full version | Windows 7, 64-bit