The ER error code is common to Frigidaire dishwashers, and it indicates a touch/key pad issue. In fact, these dishwashers are known for their integrity.
First, it is advisable to try to reset a dishwasher. In most cases, the resetting helps, at least temporarily.
In case whereby it does not work, there is a problem with the keypad. Disconnect the washer from the mains and undo the screws fixing the control panel and door panel. Once the upper parts of the control panel and door panel are off, you will see the touch-/keypad assembly with numerous plug-and-play connections.
You can try to fix the problem using an eraser: rub the ribbon cable is connected to the control board. One reason why it is worth trying is because it is very easy and not costly at all. If this does not help, replace the keypad. This is not hard to do either: all you need to do is undo a few screws. All connections are plug-and-play type. Before disassembling it, it is advisable to make a picture of the connections or write them down in a notepad.