I’m using NLP v.2.0.0 under Windows 7 (x64) in Lightroom 8.4. I have some B&W scans made using VueScan in multiexposure mode and saved as 16-bit Gray TIFF and VueScan RAW, in straight TIFF and also DNG, all saved by VueScan.
When I try to process either of them using NLP, I select either TIFF/JPEG Scan or Vuescan RAW DNG, put color mode to B&W and click on Convert Negative, I get this error at about 50-55% progress bar position.
I tried some other settings of color mode and source but the result is the same. Please let me know if you need more information.
UPDATE: I tried to process the same files under OSX, same Lightroom version and it worked well in with all NLP settings I tried.