Can't mount iso image on virtual node

[Mayuresh <mayuresh%acm.org@localhost>]

I want to examine the contents of an iso I created for burning by mounting
the iso image.


I followed instructions from:
http://www.netbsd.org/docs/guide/en/chap-rmmedia.html#vnconfig

# vnconfig  -c vnd0 newsession.iso 

When mounting, I get invalid argument error:

# mount /dev/vnd0a /mnt/tmp
mount_cd9660: /dev/vnd0a on /mnt/tmp: Invalid argument


OS: NetBSD 6.0 BETA, GENERIC kernel

# disklabel /dev/vnd0a 
# /dev/vnd0a:
type: vnd
disk: iso partition
label: fictitious
flags:
bytes/sector: 512
sectors/track: 32
tracks/cylinder: 64
sectors/cylinder: 2048
cylinders: 55
total sectors: 114624
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:    114624         0    ISO9660       0             # (Cyl.      0 -
55*)
 d:    114624         0     unused      0     0        # (Cyl.      0 -
55*)
disklabel: boot block size 0
disklabel: super block size 0


I don't know whether it matters, though the iso is created for
multisession cd writing with command:
mkisofs -J -R -o newsession.iso -M /dev/cd0a -C 63219,81016 <somedir>

What could be the reason for mount error and how to rectify?

Mayuresh