The Isolation Start-up Warning error message is frequently caused by some power loss on the DC (solar) side of the system and not the inverter itself. Sometimes in humid or wet conditions, moisture can enter the back of the panels, isolators or cable connections. As moisture conducts electricity, some power is lost, however your inverter is still producing power. The inverter is simply noticing and alerting you to a problem in the system. The red LED (Earth Fault) is lit once the isolation resistance drops below 600kOHM.
Please note, when this error message is being displayed, don’t make contact with your system or anything that could conduct electricity around your system as the DC power can potentially be fatally dangerous (you should contact your installer).