I am a second shooter and when the photographer I work for goes to import my images into Lightroom on her computer, it says there's an error and it won't import them. I shoot Nikon and she shoots Canon so I don't know if that has something to do with it, but our file handling preferences are the same and I can upload the images into Lightroom on my computer without a problem. She has Lightroom 4 and I have 5, but I still don't think that should make a difference. Anything I'm missing?
Each new camera body uses a brand new file format even though they all share the same file extension.
It would appear that your camera was created after LR 4 was released, so LR4 does not know how to read the "new" files.
Your LR5 came out after your camera was made, so it does know how to read the files.
Short of her upgrading LR4 to version 5 or 6, she will need to download a newer version of the DNG converter, then convert your NEF files to DNG files then import the DNG files.
What are the cameras models used? It is possible that the camera is newer than Lightroom 4 and so that version doesn't have support for the raw. If that's the case, the person using LR4 will need to be upgrade to a newer version or the images converted first to DNG.