older sessions crash while loading PT 7.2

[gilmour123]

Am running PT 7.2 HD2 on Mac OSX 3.4.6, dual processor G4 running at 867mhz, with 768ram. I use external SCSI drives, as I have for years. Any new session is fine, I have recorded 16 tracks at once and had no problem or lag with recording or playback. Any PT 7.1 or 7.2 session loads fine from the SCSI drives, but anything older (and I have sessions running back to 5.1) causes a crash, always. Only ProTools crashes, the Mac says it's fine.
I have tried importing the old sessions into 7.2 rather than opening them, and that crashes as well. I have updated the ATTO firmware for the SCSI interface, and while I haven't gotten the legacy hardware recognized (1622 into a 96io), I don't think either are the problem. 7.2 loads fine by itself when it's icon is clicked. Anyone? Bueller?