PowerBook G4 "The underlying task reported failure on exit (-9972)"

PowerBook G4 1.67 15" (Al), Upgraded to 1GB RAM.

Was working fine, running Leopard. Put it on shelf 4 months ago, tried it 2 days ago.

System booted, but everything stopped when I tried to launch an app. Or, for example, update would start, then hanging.

Tried to re-install. Same thing.

I ran diskutil from single user use following this guide and it reported that "The volume Macintosh HD appears to be OK".

Although, as it was checking, it reported "{ 41 910440} UniNEnet::restartReceiver" - is this normal?

Then I tried checking permissions - it quickly went to 100% and then:

Error detected while verifying/repairing permissions on disk0s3 Macintosh HD. The underlying task reported failure on exit (-9972).

So then I did fdisk -ia boothfs which appeared to complete OK and the partition table looks OK. -t confirmed this.

However, all that happens now is that it boots from the Leopard install disk, asks me the language, and then hangs with the Spinning Beachball of Doom.

I'm sure the DiskWarrior sales team will be along any second now, but given that it would cost me twice what I could hope to get for this Mac on ebay fully working, it ain't gonna happen! So is there ANY formatting or disk wiping command, boot disk/USB or utility I've missed which will avoid the final option of prising apart the PPC Powerbook the get the hard drive out and either replace (spare 120gb HDD here) or stick it in a PC and format that way?

Thanks!