This is a portal clone of the HCM issue identified by Nicolas here: SYSADM and PEOPLE password life time The resolution is identical and is listed here: http://gasparotto.blogspot.com/2010/03/psovm-sysadms-password-policy.html.
The following text is copied from Nicolas's report against HCM. The portal issue is identical:
There is a password lifetime on SYSADM and PEOPLE users which make the application and batch server stop to startup (and AppDesigner/DataMover connection impossible) when reaching the expiration limit or even grace time. They are coming within the DEFAULT profile of the Oracle database default settings. As I explained on my blog - http://gasparotto.blogspot.com/2010/03/psovm-sysadms-password-policy.html - these settings should be removed, and if needed, it must be done manually in a defined maintenance window, but certainly not "sometime" when it is not expected.
Would it be possible to change the default settings ?