I've had problems with ViewNX2 (last version). It displays thumbnails for NEF(s) from the wrong folder. When I click the thumbnail the correct NEF is previewed. I could easily delete an NEF based on see the wrong thumbnail being displayed. I've stopped using ViewNX2 on Windows 7.
....
I've had this a few times.
I think(not 100% sure) why this happens is the thumbnail cache becomes too large, and possibly corrupted/confused or something like that.
If you haven't configured the cache location, then Nikon usually places it in some user appdata type location of their choosing.
You can determine this by delving into the Options menu in VNX2(Edit->Options) and under the General tab up the top.
It'll be quite obvious once you're in this settings option.
They allow you to set the location of the cache to one of your own choice too.
VNX2 and CNX2 both operate better when all files being worked with are located on the fastest drive possible, so changing this from the default can always be a good thing.
If using mechanical drives, it's usually best to use a reasonably fast
and separate drive to help speed those programs ability to render images quickly(HDD latency).
If you're working off SSD type storage, you won't see any benefit by using a separate drive.
Under this General tab in the Options menu, you will see an option to 'clear cache'.
I've found that this usually doesn't resolve the issue(quoted above), and that deleting the cache files manually is usually best.
If you can locate the cache, go to it manually in Windows file explorer and look for various files with the extension .nkd and .nki
There may be about 8 or 10 of them in total, and named variously such as file/folder/large/medium/small .. or words to those effects.
It's safe to delete them all as they are only thumbnail cache files.
Make sure VNX2 is not running at the time tho.
What will happen tho, is that upon opening VNX2 after you've deleted them all, it has to rebuild all the cache files from scratch(a good thing if the cache has become corrupted!).
So initial loading of all images is a bit slower. Once the new thumbnail cache is built up again, subsequent uses of VNX2 will show speedier rendering of images.
Hope that helps.