PANIC: btree_split_redo: lost left sibling?

Greetings,

Our postgres system crashed and upon restarting it our database had the following errors. The error log was 4.5 gigs which is much larger than usual. We looked online for information about lost left siblings and how to fix the data and not lose the 400 million records we have. Anyone have an idea what's the matter and what the fix is?

LOG: database system was interrupted while in recovery at 2004-08-17 08:59:41 PDT
HINT: This probably means that some data is corrupted and you will have to use the last backup for recovery.
LOG: checkpoint record is at 326/C007B778
LOG: redo record is at 326/BD899570; undo record is at 0/0; shutdown FALSE
LOG: next transaction ID: 46922114; next OID: 133662911
LOG: database system was not properly shut down; automatic recovery in progress
LOG: redo starts at 326/BD899570
PANIC: btree_split_redo: lost left sibling
LOG: startup process (PID 9038) was terminated by signal 6
LOG: aborting startup due to startup process failure

Thanks,

Andrew