[SunHELP] panicbuf when booting from cdrom

[Leslie V Brigance]

Trying to boot an SS20 from cdrom - from ok prompt enter:
     boot cdrom

goes thru post & memory check and then aborts with error

     (Can't deduct panicbuf from physical memory list) program terminated.

and takes me back to the ok prompt.
Cdrom is id 6.
bootprom release is 2.15
Should I be specifying a particular slice on the cdrom?
Never had to before and I've built or repaired quite a few SS20s.
I have done a set-default on this box an still get the same error.

Is this error familiar to anyone?
Sure would appreciate some clue.

TIA