False NEF corrupted files

[Claude_C]

I have 2 computers with Lightroom.  Adobe 6.14 with No 1 = windows10 and No2 windows 7.  Lately,  some NEF files appeared corrupted (and more appear each time I open a directory) on computer no 1 (they're all on external HD).  I first Thought it was the external HD and then the computer itself.  No problems on this after scanning.  I plugged the HD on computer no2 and all NEF files that appeared courrupted on the first computer are OK and I can edit them.  Note that on the second computer it's an old and different catalog.  Anyone have ideas on how to solve this ?  Is this the catalog ? the preview ? can I recreate only the preview part and save the tagging (not losing the tagging)?  A friend of mine is suggesting me that it could be the editing RAW/NEf Files that is corrupted. how can i reset this.  Note that the problem first appeared when i did a text searchable field on a 4TB HD.  Never had a corrupted file before.

Thanks! 

[Claude_C]

Well, my mistake!  Same files where corrupted on old drives.  When you try to edit they look fine and then... color lines everywhere.  It take times to generate the preview.  When you look at them on the library module on computer no 2 they're ok even when zoomed.  When you switch to Develop and edit, you see the color bar. Well corrupted files I never knew about from the start!  Thanks anyway, if this can help someone!

[dj_paige]

This is almost always hardware related. On one computer, the USB port where you plug-in the external HD could be the problem, or it could be the memory chips, or the bus on the motherboard.

Also, please be more specific, are the photos appearing corrupted in the Library Module or in the Develop Module? If it is in the Library module, then it could also be the previews, which are stored on the hard disk (not the external HD), meaning that perhaps it is the hard disk that is the problem.

UPDATE: If it is happening on both computers, then it could be the EHD or the USB cable on the EHD that is the problem. 

[Jao vdL · Accepted solution]

It is highly likely your NEF files are corrupted for some reason. This could be hard drive failure or they could have been corrupted fom the get go. It is possible to extract the jpeg previews that are built in to every NEF file using the exiftool utility if your raw files are actually corrupt. You can test if it is the raw files themselves by opening them in Nikon NX-D and forcing it to render from the raw data (at opening it shows you the jpeg preview). 

[Claude_C]

Thanks for you're reply.

You are right.
I have numerous backups so I located a drive with ok files and the culprit
drive from which backup was made on another drive. I will be able to
salvage the files. One drive was corrupted. On the library panel, color
bars (corruption sign) did not appear. It's within the develop panel where
you can see first the corrupt files. Once the NEF is open in the develop
panel (preview files i think) the weird color bars appear in the library
panel.

I'm really glad to have numerous HD and two without errors and files
intact! Backups are important!

[Jao vdL · Accepted solution]

The importance of good backups cannot be overestimated. Incredibly important and glad to hear you had good backups. Hard drives fail all the time.