There are many variables that can affect the link between the Ethernet Extenders. Some common problems can be the wiring between the units such as a cut or open short on the line, coiled line, equipment failure, noise on the line or incorrect/loose wiring on the RJ-11 head. To verify cable or equipment failure, simply connect both units side by side on a table and verify if they link with the correct ports using the provided RJ-11 cable. If they do link, you may have faulty wiring. If they are unable to link at this point, please contact us immediately.