Extend AirPort Extreme, Unexpected Error

Thank you for your help. I have two of the current Airport Extreme Base Station models. One has my network set up already, and my phone and MacBook both come across the same error. When I attempt to extend the network, as per the instructions, an unexpected error occurs as I am told the settings on the Airport Extreme with the existing network are being read. I tried resetting my the intended extender and unplugging it, then plugging it in again. Upon turning it on the amber light is solid, then begins and continues to flash.