The NEF files from your camera require LR6 but you should be able to convert to DNG with 9.1
Have the files been passed through any Nikon or other transfer software?
Try shooting a few new raw files and add them directly to a folder from your camera or card reader.
Then batch convert the folder in DNG 9.1 by choosing source and destination folders.u
Yeppp, really good 99Jon. I upgraded to Lightroom CC and everything worked very well. Thank you so much!