[CentOS] Disks do not mount at boot

I have a problem with two entries in my /etc/fstab. When I boot the
machine, the disks are not mounted. When I give mount -a, all disks are
present without an error. Of course I don't want to manually do that
after each reboot. What can be the problem?

CentOS 5.2

cat /etc/fstab
/dev/vg/centos          /                       ext3    defaults        1 1
LABEL=/boot             /boot                   ext3    defaults        1 2
LABEL=zele_common       /dczele01/              ext3    defaults        1 2
LABEL=users             /dczele01/users         ext3    defaults        1 2
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/dev/vg/swap            swap                    swap    defaults        0 0
arend:/home             /home                   nfs    
proto=tcp,nfsvers=3,bg,defaults        0 0
arend:/program          /program                nfs    
proto=tcp,nfsvers=3,bg,defaults        0 0


Instead of LABEL I also tried to use the device /dev/vg2/users. The
filesystem is created on a logical volume, part of a new volume group:
lvs
  LV          VG   Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  centos      vg   -wi-ao   6.91G
  swap        vg   -wi-ao 992.00M
  users       vg2  -wi-ao  50.00G
  zele_common vg2  -wi-ao 100.00G

After booting /etc/mtab and mount do not list the /dczele01 entries. In
the log I see these lines:

Mar 24 08:42:02 fsutrecht kernel: md: Autodetecting RAID arrays.
Mar 24 08:42:02 fsutrecht kernel: md: autorun ...
Mar 24 08:42:02 fsutrecht kernel: md: ... autorun DONE.
Mar 24 08:42:02 fsutrecht kernel: device-mapper: multipath: version
1.0.5 loaded
Mar 24 08:42:02 fsutrecht kernel: EXT3 FS on dm-0, internal journal
Mar 24 08:42:02 fsutrecht kernel: kjournald starting.  Commit interval 5
seconds
Mar 24 08:42:02 fsutrecht kernel: EXT3 FS on sda1, internal journal
Mar 24 08:42:02 fsutrecht kernel: EXT3-fs: mounted filesystem with
ordered data mode.
Mar 24 08:42:03 fsutrecht kernel: kjournald starting.  Commit interval 5
seconds
Mar 24 08:42:03 fsutrecht kernel: EXT3 FS on dm-3, internal journal
Mar 24 08:42:03 fsutrecht kernel: EXT3-fs: mounted filesystem with
ordered data mode.
Mar 24 08:42:03 fsutrecht kernel: kjournald starting.  Commit interval 5
seconds
Mar 24 08:42:03 fsutrecht kernel: EXT3 FS on dm-2, internal journal
Mar 24 08:42:03 fsutrecht kernel: EXT3-fs: mounted filesystem with
ordered data mode.
Mar 24 08:42:03 fsutrecht kernel: Adding 1015800k swap on /dev/vg/swap. 
Priority:-1 extents:1 across:1015800k

Then I give a mount -a and see this in the log:
Mar 24 08:44:28 fsutrecht kernel: kjournald starting.  Commit interval 5
seconds
Mar 24 08:44:28 fsutrecht kernel: EXT3 FS on dm-3, internal journal
Mar 24 08:44:28 fsutrecht kernel: EXT3-fs: mounted filesystem with
ordered data mode.
Mar 24 08:44:28 fsutrecht kernel: kjournald starting.  Commit interval 5
seconds
Mar 24 08:44:28 fsutrecht kernel: EXT3 FS on dm-2, internal journal
Mar 24 08:44:28 fsutrecht kernel: EXT3-fs: mounted filesystem with
ordered data mode.

So from the log it looks like the mount is done, but nothing is actually
mounted. I'm puzzled.
The nfs shares and the /boot drive are mounted correctly. So what could
cause these two shares to not mount automatically? What else can I do to
debug?

Thanks,
Theo