Just stumbled on this incident as a matter of interest:-
Airbus A320-232, G-MIDW
Summary:
The aircraft was established in the cruise at FL380. A warning of excessive cabin altitude was displayed on the ECAM (Electronic Centralised Aircraft Monitoring) screen. However, the display showed the pressurisation parameters, including the cabin altitude, as normal so the crew believed that the warning was spurious, although they donned oxygen masks as a precaution. Eighteen minutes later they were advised by the cabin crew that the passenger oxygen masks had deployed and they initiated an emergency descent to FL100, at which level the flight continued to its destination without further incident. A fault was later found within the System 1 Cabin Pressure Controller and the manufacturer is reviewing the system architecture to establish how misleading information was displayed to the crew.