Safari Doesn't See Webplugin

I've downloaded and insalled the SurveilClient HiDvrPlugin.webplugin for my Swann security system so that I can monitor my cameras from my laptop. Everytime I go to my cameras IP address, I've given the following message:

When I check Help > Installed Plug-ins, Safari doesn't even show HiDvrPlugin.webplugin in its list of installed plugins. Is there a way I can manually install the webplugin so that Safari recognizes it? The plugin is currently installed in the Macintosh HD/Library/Internet Plug-Ins directory.