Have any of your apps experienced "shutdown immediate" for no apparent reason?

Recently, our production database did a shutdown immediate. There No errors in the alert log. We checked /var/adm/messages, and the VCS log. The VCS log indicated that it could not access the listener. The listener log indicated that it could not access the database. Now we are not sure if VCS played a role in this but the Oracle database shows no errors, core dump - nothing.

Any experience or insight?