Sorry to say but you have kinda missed the boat on that.
Aperture is now 3+ year discarded by Apple? In other words No longer supported in any way by Apple for about 3+ years. And that plugin was written to work with older version of Lr, the traditional version.
I think you have 2 options.
1) In Aperture Export all your images as TIF files to retain the most quality of the images and edits you may have done in Aperture and then import those TIF images into LrC. Along with that get all your images out of the Aperture created Package folder (looks like a file but it is really a folder that you need to Expand) that is holding all your images. That is if you didn't set the option to store your images in regular folders on your hard drive. And then import those along side the Exported TIF files created earlier.
2) As above getting your images out of the Aperture (Photos/iPhoto) package folder and then import just those images into LrC.
Doing #2 will remove any edits you have ever done to them in aperture and lose any collections/Albums, or whatever it is called in Aperture, but will give you back all your original images.
Doing #1 will at least preserve your edits in the TIF files and give you back your original files.
If you never let Aperture place your original images inside that package folder, You had Aperture place your images in folders someplace on your hard drive then just Import them into LrC from where they are already stored on your drive using the ADD option at the top of the LrC Import window to Add them to the LrC Catalog file and Leave them where you originally placed them.
Google translation: "I want to migrate my Aperture libraries to LR CC 9.4. Unfortunately, the import dialog in the plugin is inactive. How can I access the Aperture Library?"
You must have at least one photo selected before you can invoke the plugin (it's a bug). If you've got an empty LR catalog, import a photo and select it before doing File > Plug-in Extras > Import From Aperture Library.
The plugin isn't well implemented and has had serious bugs from the beginning (shame on Apple and Adobe). But it should still work with LR 9 and LR 10. Beware that due to the poor implementation, it gets progressively slower the more photos you import at once, such that an Aperture library of tens of thousands of photos could take days (literally). You can work around that by breaking it up your Aperture libraries into smaller libraries of, say, 5K photos each.
See this article for tips on importing from Aperture and a fallback method if you can't get the plugin to work: