failing 8.1.4 autovacuum

I have an 8.1.4 autovac process running on HP-UX 11.23 IA64 and
repeatedly failing with the following error:

    ERROR:  failed to re-find parent key in "audit_idx1"

Will a reindex or drop index make this problem go away?

Is there anything I can do to help identify the underlying issue?
(This is an intensely used production system, so I have very
limited room to operate.)

TIA.

Ed