I am trying to import my Aperture Library into Photoshop Lightroom. I'm using a referenced library with Aperture and want to maintain the same directory structure in Lightroom. I have over 1TB of pictures so I just want to leave the images in place. I've selected the Leave reference images in their current location and started the import process using Import Plug-in in Lightroom 6. It creates the correct directory structure in the new catalog but only imports a few of the images and ends with "bad argument #1 to '?' (string expected, not nil)". Suggestions?
Running iMac with OSX v10.10.3. with Lightroom 6.0 and Aperture v3.6
Referenced images are best, as it sounds like you are setup to do. Suggest you run a permissions repair and library repair to correct issues. Some folks have had to split up their library into chunks to see what fails. You might try that as a test first. Export a subsection of your library and see if you can get the plug-in to work. If you do, then it is likely a permissions or library corruption issue.
Not to say there may not be other issues, but that seems to be the most common problem.