Try copying the files locally into a folder then proceed to convert them using the DNG converter.
How did you transfer the images from the card to your computer? There have been many complaints about using the Nikon software to transfer images, better to either configure your camera to appear as a disk drive, or best (IMO) use a card reader to directly transfer images.
Also verify you're using version 7.4 of the DNG converter.
Thank you, Adrianna. That worked, although I could swear I tried that earlier. Any specific reason why that happened?
I just popped the sd card into my imac and duplicated them. That is how I always do that, they use PS CS 5 to work. I tried a card reader, that didn't make any difference. I am using the 7.4. The above suggestion did work, copying the files to a local folder. Thank you.