I had no problem opening a Nikon 610 NEF file in my version or Rawtherapee. Perhaps yours is too old ?
You should post one of ‘problem’ files via file serving server, so we can check your file. What are NEF settings in the camera Compression ? 14 / 12 bit ?
Mine is:
Branch: gtk3 Version: 4.2.927 Processor: core2 System: Linux Bit depth: 64 bits
@tius upload one of those files using http://filebin.net/ and paste the full link here, then we can take a look.
here the file:
http://filebin.net/jqidq84xf4
I use 64 bit Trisquel GNU/Linux 7.0 Belenos.
My RT version is 4.0.12.0
Thanks.
I confirm tius’ problems:
Neither win 7/64-bit RT 4.2.927 nor
Ubuntu RT 4.2.937 can open the file.
RT just shows the “duotones” presented in tius’ first msg.
(Poggibonsi? Close to Firenze?)
7 MB file size for 24 Mp? Maybe it’s corrupted?
It looks, there is not much more than a 24 MP jpg in this file.
Grrr - how could I have missed to check file size of tius’ file? 
Rename nef to jpg and it will open.
ExifTool says Error: Not a valid TIFF (looks more like a JPEG) - basket_20160409_poggibonsi_vs_msb_001.nef
With metadata stripped, it still has 6,5 MB. IrfanView also recognises it as a jpg with incorrect extension.
I do not know what could have happened grrrrrrr…
I did not noticed the size of the files.
Now I try to rename to see if it works.
Yes Claes, about 40 km.
Ok, now RT 4.2 work.
The images are renamed.
I just have to understand why the pictures have been reduced in size and changed in format.
And… Learn to use RawTherapee, of course.
Thanks to all and
have a good light!
Ciao.
@tius RT does never modify your files! So the reduced size caused by being them jpeg and not nef must have happened elsewhere.
I did not understand where I went wrong. Patience 