Have you tried deleting it through My Computer? sm

I've run into this, and I'm thinking that was how I got rid of it. But I was not running Windows XP when I last used WP51, and it's been about 4 years. (I had to switch to Word about then, and then I retired 2 years ago.)

I believe this is a print job that somehow didn't print or get into the queue.

If this doesn't do the trick, try the DOS Forum at WordPerfect Universe. The people there are great at helping with all sorts of WP51 problems.