[SunRescue] HELP: Cannot assemble drivers for root problem

[John Lengeling]

I have an Ultra 1/140 Solaris 2.5.1 with a bad fan so I called Sun and
instead of sending me a new fan, I received an entire Ultra 1/170E
motherboard.

After swapping the motherboard, I get the following error message:

Cannot assemble drivers for root....
Cannot mount root on ...

Then the system halts.  I tried doing a "boot -r" but that didn't help. 
How can I tell the system to boot with a generic kernel and rebuild
itself and the device entries...

johnl