When trying to delete a Class using IDE (simply right click and delete, and confirming I want it deleted in SF as well), it fails with the following screenshot. I have seen a couple posts via Google search that show people having this problem, but I'm not seeing a solution.
I am trying to cleanup. We have consolidated many classes (and triggers) into single classes/triggers, and now have old classes commented out with no code actually running - we'd like to remove them so our list of classes/triggers is clean/shorter.

Trying the same in Sandbox: Worked fine. I tried deleting from Production AFTER deleting in Sandbox, and it still failed.