E2 error using Generator with Progressive Industries EMS

The error is because the generator has no neutral-ground bond like the main utility breaker panel.

You can use bypass or make a bonding plug. To make a bonding plug... get a replacement plug from the hardware store. Get a 100,000 ohm 1/2 watt or 1 watt resistor from the electronics supply house. Connect the neutral and ground pins within the plug. No cord gets attached. Insert the plug into one of the generator outlets and the error will clear.