how do i change access privileges on a file

I have a bizarre problem with an old file on my computer. It is a collection of images stored on a PowerPoint file, and has been on my computer for several months. Today I was editing the file and I suddenly got this error code 43. Afterward, I was unable to open the file, so I immediately went to my Time Capsule and restored the file from a backup done a few days ago. SO, I figured I'd delete the old one that was giving me "code 43" fits. Unfortunately, I couldn't delete the file, because I got this same error code, and was told that the computer couldn't move the file to the trash.

After a little research on this error code, I discovered that it originates with some file-sharing permission issue. When I went to my "Finder", right-clicked on the file name and click on "Get Info", I see that, at the bottom of the menu box, my "Sharing & Permissions" area says: "You have unknown access."

How do I correct this problem and remove the error code so that I can trash this file?

Thanks.

D Perry