Ah ok, I think I see what has happened. There's a bug with the support for crossfading with old-style PlayMusic commands -- and as the crossfading was updated to the new audio system in beta 3, that explains why it broke at that point.
Please try this engine:
http://www.adventuregamestudio.co.uk/acwin.zip
and let me know if it fixes the problem.
Please try this engine:
http://www.adventuregamestudio.co.uk/acwin.zip
and let me know if it fixes the problem.