I took some pictures on a friends Nikon D750. She is looking to sell and I am thinking of upgrading. I was able to get them onto my computer, but when I went to import them into Lightroom, it says "These files are not recognized by the RAW format support in lightroom". I had some issues before when I shot in RAW on my Nikon D3300 but I simply ran them through the DNG converter and they uploaded. When I tried to run these images through the DNG converter, I get this rejection: "The source folder does not contain any supported camera raw files."
Any ideas?? My friend uses Lightroom 4 just like me and she has never had an issue.
You need to upgrade your software do read the new file format from the D750.
To natively read the D750 files, you need Lightroom 5.7 or newer, ACR 8.7 or newer.
To stay with your LR4, you could download the newest DNG converter and import the DNG files after converting the NEF files.
When using the DNG converter, you choose the folder containing the NEF files. But you don't open the folder. The DNG converter works at the folder level. Additionally, you will need DNG Converter 8.7 or newer in order to support the files from the D750.