Diagnosis
The main temperature sensor in the cooking chamber has failed or is disconnected. This is a common failure point.
How to Fix It
Unplug the unit and let it cool completely. Remove the cooking racks, pan, and rotisserie basket. Look for the small silver probe near the top rear heating element. Check that its wire is firmly connected to the main board. If it is, the sensor is bad.
If That Didn't Work
The main control board can also throw an Er1 if it fails. If the sensor connection is solid, the board is likely the issue.
Heads Up
Do not attempt to bypass this sensor. The unit will not operate without a valid temperature reading for safety. This repair usually requires a technician or replacement.