Ok. New development in the problem.
If I delete files from my Mac hard drive, they delete just fine. If I try to delete them from an external hard drive, they don't delete. That's when I have the problem discussed above.
Any suggestions for what to do at this point? I restored permissions like you suggested for my computer's hard drive, but it isn't an option to do it for my external hard drive. And I know I've used PM before to delete files off of a hard drive, including this particular hard drive.