The Steam build of the game depends on this plugin, but so long as the plugin exists on disk in the same location as the game, there is no situation I'm aware of (as the author of the plugin) that would cause AGS to fail to load it. There are not any fatal errors that would be generated from the plugin failing to communicate with Steam or anything like that either, so I'm somewhat perplexed as to what would be causing this.
This happens every time you run Gemini Rue?