ntz1111, I have moved your post to a new thread so that it will be more visible. I am also requesting an Admin to change your screen name for your own protection. It is not advisable to have your email address displayed as your name.
As for your problem. is it possible that the DNG files have previously been imported into the catalog? And what OS are you using?
In order to troubleshoot the problem, try creating a new catalog and see if you can import the files into the new catalog.