repair corrupted files (dng)

When you ran “Check DNG” and found those 2 invalid files, were you able to open the original NEFs outside Lightroom? Just wondering if those are intact or maybe partially corrupted too.

Also, not sure if anyone’s mentioned this already, but have you tried checking those problem files with any jpeg repair software (just in case the embedded previews are causing the hiccup)? Might sound odd since it’s DNG, but sometimes those previews get corrupted and throw weird errors.

After you get the image files restored from backup, make sure you do a deep scan of the hard drive for bad sectors.

How do you know that the RAW files, the NEF files are not corrupt?

If you inspect them in camera, you are not seeing the RAW data, you are seeing an embedded JPEG.

If you inspect them in a file manager, you are looking at the embedded JPEG not the RAW data

If you look at them in the Import screen in LrC, you are seeing the embedded JPEG, You will not see a translation until after previews are created

If you look at them in Adobe Camera RAW, you are looking at the embedded JPEG, you will see an issue when you convert.

I can't recall when it was added, but you can use the 'Validate DNG Files' (see Library module Library menu) to find any others that may be corrupt. When you find the files you'll likley need to convert the original NEF files to DNG, then subsitute them back into the folder containing the damaged DNGs. Remember, that the new DNGs must have the same file name ans the damaged files. If you copy/paste using OS tools the original metadata and edits stored in catalog can be saved back to the new DNGs. 

Restore the photos from backups.