We have just been informed that SoundSwitch 2.9 has been released, with a new option to output Art-Net to "localhost" (the same computer).
There is a new check box in the Hardware tab under Preferences called "Localhost Art-Net Node" that you need to check if you are running Capture on the same computer as SoundSwitch.
It would appear that you need to start Capture before you start SoundSwitch. We will let the team behind SoundSwitch know so they can fix it.