vfs_mountroot: can't open root device / cannot mount root, error = 6

[Bill Blass <baringskiier%yahoo.com@localhost>]

Can somebody please help me out here?  I'm new to NetBSD and was wondering if 
anybody has an idea why I have to specify the root and dump device by hand 
during boot.  Here is a snippet of the boot situation I'm referring to:

<snippet>
wd0 at atabus0 drive 0: <SanDisk SDCFH-256>
wd0: drive supports 1-sector PIO transfers, LBA addressing
wd0: 245 MB, 980 cyl, 16 head, 32 sec, 512 bytes/sect x 501760 sectors
wd0: drive supports PIO mode 4
boot device: <unknown>
root on wd0a dumps on wd0b
vfs_mountroot: can't open root device
cannot mount root, error = 6
root device (default wd0a): wd0d
dump device (default wd0b):
file system (default ffs):
root on wd0d dumps on wd0b
init path (default /sbin/init):
init: trying /sbin/init
....
....
</snippet>

I'm creating my Compact Flash disk image (for my 256MB SanDisk) as follows:

# dd if=/dev/zero of=netbsd.img bs=512 count=500400
500400+0 records in
500400+0 records out
256204800 bytes transferred in 6.666 secs (38434563 bytes/sec)

# vnconfig vnd0 netbsd.img

# fdisk -ua0 vnd0
fdisk: primary partition table invalid, no magic in sector 0
fdisk: Cannot determine the number of heads
Disk: /dev/rvnd0d
NetBSD disklabel disk geometry:
cylinders: 244, heads: 64, sectors/track: 32 (2048 sectors/cylinder)
total sectors: 500400

BIOS disk geometry:
cylinders: 244, heads: 64, sectors/track: 32 (2048 sectors/cylinder)
total sectors: 500400

Do you want to change our idea of what BIOS thinks? [n]

Partition 0:
<UNUSED>
The data for partition 0 is:
<UNUSED>
sysid: [0..255 default: 169]
start: [0..244cyl default: 32, 0cyl, 0MB]
size: [0..244cyl default: 500368, 244cyl, 244MB]
bootmenu: []
Do you want to change the active partition? [n] y
Choosing 4 will make no partition active.
active partition: [0..4 default: 0]
Are you happy with this choice? [n] y

We haven't written the MBR back to disk yet.  This is your last chance.
Partition table:
0: NetBSD (sysid 169)
    start 32, size 500368 (244 MB, Cyls 0-244/21/16), Active
        PBR is not bootable: All bytes are identical (0x00)
1: <UNUSED>
2: <UNUSED>
3: <UNUSED>
Bootselector disabled.
Should we write new partition table? [n] y


# disklabel ie -I vnd0
# /dev/rvnd0d:
type: vnd
disk: vnd
label: fictitious
flags:
bytes/sector: 512
sectors/track: 32
tracks/cylinder: 64
sectors/cylinder: 2048
cylinders: 244
total sectors: 500400
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

4 partitions:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a:    500400         0     4.2BSD      0     0     0  # (Cyl.      0 -    244*)
 d:    500400         0     unused      0     0        # (Cyl.      0 -    244*)
~

# newfs /dev/vnd0a

<installing files here>

# installboot -v -o console=com0,speed=57600,timeout=0 /dev/rvnd0a 
/usr/src/sys/arch/i386/stand/bootxx/bootxx_ffsv1/obj/bootxx_ffsv1

# vnconfig -u vnd0


Do I need to do something differently?  I've searched this topic on google for 
a couple/few weeks now and haven't figured it out, so hopefully somebody on 
this list knows.

Thanks,
Bill