The error itself is descriptive and self-explanatory, and you might suspect that a hardware problem occurred with the system's blower or fan assembly located at the top-most rear of the system cabinet.
Upon further investigation you note that the blower is indeed spinning at a good rate. Given that, you should then check to see if the "AC Dist to Blower to Filter to Keyswitch Harness" plug/adapter is plugged in correctly. Two cable assemblies connect the blower assembly to the unit's power supply. One is the "power supply" cable and the other is the "AC Dist to Blower to Filter to Keyswitch Harness."
Once the harness is securely connected, you see another message, NOTICE: FAN RECOVERED, logged on the system's console screen, or, if missed, it is in /var/adm/messages.