Using iMac OSX 10.9.5 with Lightroom 5.7.2 - and unable to load plugin for tether-nikon-plugin.lrplugin 18.104.22.1681162 (Silver Effex). The software has been successfully downloaded and shows as "installed and running" in the Lightroom Plug-in Manager. When I attempt to "add" plugin I receive the error message: "An error occurred while attempting to load this plug-in."
Same error message received if I should attempt to "add" other plug-ins that were provided by Lightroom. Only exception is the Aperture/iPhoto importer plugin that was downloaded as part of the 5.7.2 upgrade loaded today.