Probe1:ata1:... keeps resetting/timing out on 12.R install attempt

[Chris]

OK I've got a Dual Proc G4/800Mhz (model 7450) I've been trying desperately
to get FreeBSD on, since releng/9. But not any success. I just spun up
the 12.R install media -- both disc1 && DVD1. But it bails on the ATA
DVD/RW I'm booting from. Always with
probe1:ata1:0:1:0): CAM status: command timeout
resets && retries...
Interestingly; OpenBSD && NetBSD don't do that, and will land at the
option to install, upgrade, drop to shell.

Any thoughts/suggestions would be *greatly* appreciated.

Thanks!

--Chris