Difference between System Exception and Portal Exception
SystemException This Exception caused by system problems. Examples include database connection errors and file not found errors. System exceptions are always unexpected , and generally indicate that the portal is misconfigured or that a critical service is unavailable. PortalException This exceptions related to business logic. Examples include invalid input, portlet errors, and references to non existent database records. Portal exceptions are generally caused by user error , and do not indicate that anything is wrong with the portal itself.