Ardour fails to start with previously working session
using Ardour 2.8.4 on Mac OS X Tiger 10.4.11 (1st generation MacBook) to convert some old Logic 7 Express projects into Ardour for additional work on GNU/Linux. Ardour fails to start (getting stuck at "Setup signal flow and plugins") with session file that worked a few hours before.
the project is pretty simple, just exporting audio regions from Logic and importing them into Ardour, a few plugins. i saved the session, closed Ardour to stop working, and left JACK OS X running. when i returned (after the computer had been asleep a few times) and tried to open the session, Ardour would start, show the splash window, flash the various start up messages on the splash window, connect to JACK (i can see the routings in the JackPilot Connection Manager), but freeze when "Setup signal flow and plugins" comes up on the splash window. the CPUs spike and just run until the process is killed. i left it running a few minutes, but no luck. no error message, etc, either.
tried rebooting, freeing up space, latest JACK OS X, etc. i figure the problem is somewhere in the session file, but i am unfamiliar with the XML the contents as of yet. can anyone point me in which parts to start editing first?
finally, this same session file opens on Ardour 2.8.2 when transferred to Ubuntu Studio 9.10.