[G4] Invalid Sibling Link

[Howard]

Been having troubles with my PowerBook G4 running 10.4.11 being  
occasionally slow. I have Applejack installed and did an auto restart  
with all that it entails but on the first test, which I can't  
remember now what it is, I got a "volume failed, invalid sibling  
link, 4, 13235. It suggested running the test over and I did several  
times but no luck. Finished manually and rebooted and system seems to  
be working as good as usual but what is the error, how does it affect  
the system and how do I fix it?

Also looking for anyone that has moved to bigger and better systems  
and has a spare copy of 10.5 available for free or cheap