error 471 detected in background process

> Got a trace file generated in bdump, and the tail is the following:
>
>
> Unix process pid: 27169, image: ora_pmon_PROD
>
> *** 2000-09-28 18:10:58.156
> *** SESSION ID:(1.1) 2000-09-28 18:10:58.090
> error 471 detected in background process
>
>
> Anyone tell me what error 471 detected in background process means?
>

The background process was pmon Received on Thu Sep 28 2000 - 22:16:40 CDT