Can't delete old backup files

I installed Windows 7 last year, 6/2013, and now I notice my external hard drive is filled with old wbverify and wbcat files from that time. I'm unable to delete them. I get a message that they cannot be found.
I turned of the automatic system backup a few months ago but these files are all from last year. There are over 1,900 files with about 400 of them with a 0 size. The others range from very small, 8kb to over 8MB. If I can delete them I can capture about a third to a half of the space. Any help is appreciated.

That was very useful information. The screenshots didn't look exactly like my screen but I was able to figure it out and delete all those files. The hard drive used space dropped down to about half of what it was, just what I wanted. I have that feature turned off so I don't expect more. I'm a writer of books and I use the built-in backup utility of the word processors.
Thank you for this help. This is exactly what I joined for.