This appears to be a corrupt file which could be a memory card going bad, a problem transferring the file (ie bad cable) or a problem with the camera's writing ability. Most likely it is the first. If you have a card reader on your computer you can run a check disk on the memory card and scan for bad sectors. If it finds any errors then your diagnosis is complete. If not, I would switch memory cards and see if it continues. Was this transferred using the camera or using the card in a reader? Also remember that depending on the processing software you are using, you may only be looking at the jpg file that is embedded into the NEF file. It is possible that the NEF itself is still good.