Explanation
Be sure that you are running Net3 Concert software v4.0.2 or newer. The Response Mk2 gateway device package was not added to Net3 Concert until v4.0.2. Any older version will not be able to reliably communicate with these gateways.
You can check the version of Net3 Concert by opening the 'Help' dropdown menu in the upper left corner of the software window, then choosing 'About Net3 Concert'. The version number listed in bold at the top of the pop up is the version you are looking for.