How to solve the error: "lightroom could not import this catalog because of an unknown error" when trying to "import from catalog"?

Question

I have around 400,000 photos of 15 years so given the high number, I organized all my photos into 6 catalogs to avoid potential problems. All the photos and the catalogs are in a 4TB Seagate external hard drive. I use Adobe Lightroom 5 and I use a PC with the latest Windows Office 2013.
I wanted to have a NEW Catalog of all my rated 1 Star+ photos of all the years in a single Catalog. So I created what I called Star+ Catalog and I was told the best option is to import a Catalog at a time and given that there is no means to filter importing only Stared photos, I would import all the photos and then delete all the UnStared photos. I did that for Catalog Year 2014 but at the end gave me the message: "lightroom could not import this catalog because of an unknown error". It actually had imported around 40k photos from about 50k total. I tried again and again and every time I end up with the same thing. I created another new Catalog and stared from scratch and the same ting happened: the ONLY EXACT 40k or so photos were imported and the rest were not!! When I imported Catalog Year 2013 of around 45k photos, it worked perfectly. But when I imported Catalog Year 2012 of 35k photos, the same thing happened!! 
Any advice: 1) on how to solve this? and 2) if there is a better and easier way to create this Master Catalog of All Stared Photos of All my Catalogs?

Answer 1

OK, my starting point is that LR can happily contain 400000+ photos, and it's a mistake to create a 1 star plus catalogue as you suggest. Instead, I'd recommend you create a master catalogue of all your photos, which you can then query however you want - 2 star, or a certain keyword, or with "xyz" in the title etc.
If you are intent on going that way, you could try a slight change from what you've done so far. Instead of trying to import an entire catalogue and then delete no-star pictures, take the 2014 and 2012 catalogues and select only the 1 star photos. Then do an Export as Catalog for these items, and import the 2014-1star and 2012-1star into your new catalogue. That may get you past the problem images which I suspect are the problem.
If that doesn't work, or if you follow my initial advice, you're going to need to identify the image where the failure occurs. You may have a corrupt image file, and replacing it from your backup may be sufficient to resolve the problem. Alternatively, it may be a corrupt record in the catalogue, and in this case it may be sufficient to remove the image from the catalogue and import it again. You might try selecting everything in the 2014 catalogue and seeing if you can do an Export as Catalog, creating a clean 2014, and deleting 2014's previews folder might also get rid of a potential problem. Something else is to try the Export as Catalog for images 1-40000, then a second Export as Catalog for images 40002-50k.
So a few things you'll need to try, rather than a magic bullet, and a recommendation to change the underlying direction.
John