Problem: Since ArcMap and Responder Explorer now communicate with each other via HTML, we have to specify which ports they are going to use in ArcMap.exe.config and Miner.Responder.Explorer.exe.config. This error is caused when other applications are already using the default port that Responder is trying to use. The problem can be solved by changing the configuration files (ArcMap.exe.config and Miner.Responder.Explorer.exe.config) to use a different valid port.

Fix: Open the ArcMap.exe.config and Miner.Responder.Explorer.exe.config files, scroll to section displayed below and change 29100 to a valid port number and 29101 to another valid port number. Esure both files are updated and then restart ArcMap and Responder Explorer.