[bestgenman]

Thought i would chime in here even though it has been months since your trouble. If you were running 4 tons of basement air and one ton additional on roof, your loads are fairly significant. You stated that power was from genset at the time, if a large block of load released (shut off) the voltage regulator had to reduce excitation quickly, however there is always some overshoot of voltage and possibly the inverter caught the overshoot and displayed an overvoltage condition. Reset the inverter as Tom mentioned and watch it for a while to be sure the overshoot was the culprit.
I agree with Tom on watching your current (AMPS) since the additional roof top may not have been connected to the disabling scheme Newell uses to prevent overcurrent while the Aqua Hot is on electric heat.

Gordon