"missing operating system"

[Peter Steele]

Okay, so I've seen this error many times and its cause has always been clear. In this case I'm stumped. I've got a 3U SuperMicro server with 16 drives hooked up to two 3Ware controllers. The drives are configured into two logical drives da0 and da1. I've installed a FreeBSD 8.0 OS on da0 but when I boot the box I'm seeing this error. I've swapped the RAID slots in the BIOS boot list to make sure the BIOS has the right entry for what I think is da0 listed first.  I can boot the system with a USB stick and have verified that the OS is installed correctly:

root@:~>
# mount /dev/da0s1a /mnt
root@:~>
# ll /mnt
total 68
drwxr-xr-x  22 root  wheel   512 Dec  2 15:58 .
drwxr-xr-x  24 root  wheel   512 Dec  2 15:44 ..
-rw-r--r--   2 root  wheel   798 Nov 10 06:04 .cshrc
-rw-r--r--   2 root  wheel   182 Dec  2 11:39 .profile
-r--r--r--   1 root  wheel  6206 Nov 10 06:04 COPYRIGHT
-rw-r--r--   1 root  wheel     9 Dec  1 22:31 VERSION
drwxr-xr-x   2 root  wheel  1024 Nov 10 06:02 bin
drwxr-xr-x   7 root  wheel   512 Dec  1 22:31 boot
dr-xr-xr-x   6 root  wheel  2048 Dec  2 11:22 dev
drwxr-xr-x  21 root  wheel  2048 Dec  2 11:39 etc
drwxr-xr-x   2 root  wheel   512 Dec  1 22:31 home
drwxr-xr-x   3 root  wheel  1536 Nov 10 06:03 lib
drwxr-xr-x   2 root  wheel   512 Nov 10 06:02 libexec
drwxr-xr-x   2 root  wheel   512 Nov 10 06:02 media
drwxr-xr-x   2 root  wheel   512 Dec  2 11:39 mnt
drwxr-xr-x   3 root  wheel   512 Dec  1 22:31 opt
dr-xr-xr-x   2 root  wheel   512 Nov 10 06:02 proc
drwxr-xr-x   2 root  wheel  8192 Nov 10 06:03 rescue
drwxr-xr-x   2 root  wheel   512 Dec  1 22:31 root
drwxr-xr-x   2 root  wheel  5632 Nov 10 06:03 sbin
lrwxr-xr-x   1 root  wheel    11 Nov 10 06:04 sys -> usr/src/sys
drwxr-xr-x  11 root  wheel   512 Nov 10 06:36 tmp
drwxr-xr-x  11 root  wheel   512 Nov 10 06:36 usr
drwxr-xr-x   2 root  wheel   512 Dec  2 11:37 var

What's more puzzling to me is that I have another identical system that was purchased a few weeks ago and I have successfully installed the OS on that box without seeing this error. I'm thinking there might be some kind of BIOS setting that is different between the two boxes but I'm not really sure if that explains what's going on.

Does anyone have any suggestions what I could do to troubleshoot this problem?