Boot fails on Sun Ultra 45

I am tinkering with a Sun Ultra 45.  I tried to install NetBSD
10.1 (sparc64 port) to a new 500GB SATA SSD using the default
partition scheme.  The installer didn't produce any error messages,
and everything looked fine.

However, when rebooting, I get this series of messages from OpenBoot:

Boot device: /pci@1e,600000/pci@0/pci@9/pci@0/scsi@1/disk@0,0:a  File and args:
NetBSD IEEE  1275 Multi-FS Bootblock
Version $NetBSD: bootblk.fth,v 1.17 2022/11/17 06:40:39 chs Exp $
.Inode not directory
Evaluating:
The file just loaded does not appear to be executable.

I tried reinstalling using a root partition size of 240GB, with the
same results.

Solaris 10 that came with the machine boots fine on a 250gb spinning hard drive.
I also got OpenBSD to boot from a 250gb SSD.

Is there something I can do differently to get NetBSD to boot successfully?

Here is the disklabel:
# /dev/rsd0:
3 partitions:
#       size   offset     fstype  [fsize bsize cpg/sgs]
a: 503318272   0          4.2BSD       0     0     0  # (Cyl. 0 - 247695)
b: 16777216    503318272  swap                        # (Cyl. 247696 - 255952*)
c: 976773168   0          unused       0     0        # (Cyl. 0 - 480695*)

Thank you for any help you may be able to offer.

Steve