can't delete tasks?

We're trying to delete some duplicate tasks, but the system keeps telling us we don't have permission to do this. I'm using the Administrator role and still can't do it. I've had the people who created the tasks try to delete them, and they couldn't, either. I've checked the permission level for tasks, and it's already set to "full" under "Permissions/Lists" for me and my Sales Admin. I recently changed the Custom Sales Person's permission level to "Edit" for "Permissions/Lists/Tasks." Could this be affecting everyone's ability to delete tasks?

What are we missing?

Thanks,
Jill