Hi,
What sort of media are you recovering from? What type of search did your run?
I suggest you try the following....
When you run Recover My Files (
www.recovermyfiles.com) click on the "Manually Set Options" button on the main program screen. In the SEARCH tab make sure there is a tick in the box for "Search for Lost Files" and take the tick out of "try and determine file size of Lost Files" - now set the default file size to 16mb.
NEF files are very close to TIFF file in structure so please search for TIFF files. Once you find and save the TIFF files, then rename the extension to NEF.
This should recover your NEF photos.