Without the model number off of your refrigerator I am only able to provide you with some basic information.
This error code Er FF indicates a problem with the evaporator fan motor but it can also be with the main control board. When the power cord is disconnected for 30 seconds and then reconnected, it resets the board. Sometimes this procedure corrects the problem and sometimes it does, for only a short period of time. Usually in this case, the main board will need to be replaced. First it needs to be determined if the fan motor is running or not. If the motor is still running, the main board, which is located behind the unit, will probably need to be replaced. It's possible the motor may not be sending a low voltage signal to the board. If the motor is not running, some voltage checks will need to be made to, determine if the motor has failed or if the board is not sending voltage to the motor. These are some difficult checks to make and the motor can be a difficult repair, which will require a technician. I'm listing a site you can access, to have a technician come out to check it. Here is a link for the website:
Sears Home Services
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For more details respond to this thread with your model number and we can look into this further.