Maybe they are in a protected, i.e. "read only" folder. Can you remove them from the catalog and then delete them with Explorer/Finder?
They are in the same folder as many other images that I am able to delete.
I went to Finder and renamed the image, then I was able to delete it
Why would this problem occur - here is the name it had when I first imported it.
The file named “20141009-_DSC0172-2.NEF” could not be moved to the Trash folder.