Lost Volume Group!

After upgrading a system from RedHat 9 to Scientific Linux 4 (a RedHat EL clone) the system can no longer see my Volume Group! This isn't a system partition but a "user" one. Also, if it's relevant it was an 'upgrade' not a new install.

pvscan gives me:
/dev/cdrom: open failed: No medium found
PV /dev/hda4 lvm2 [126.39 GB]
Total: 1 [126.39 GB] / in use: 0 [0 ] / in no VG: 1 [126.39 GB]

/dev/hda4 was the only PV in volume group Volume00.

vgcfgrestore -n Volume00 /dev/hda4 gives:
/etc/lvm/backup/hda4: stat failed: No such file or directory Couldn't read volume group metadata.
Restore failed.

The file /etc/lvmtab.d/Volume00 exists, is several months old and contains optimistic strings like:

/dev/hda4
Volume00
/dev/Volume00/LogVol00

The directory /etc/lvm/ contains three empty subdirectories:

archive backup lvm.conf

Surely, if I have the Physical Volume I must be able to access the data?

Thanks in advance.

John