Using MODX 2.2.15, duplicate pages won't go away when Delete command used.
Error log, last message:
"[2015-04-28 10:42:08] (ERROR @ /connectgmha/resource/index.php) Resource URI trail-clinic-(august-28-30,-2015).html already exists for resource id = 344; skipping duplicate resource URI for resource id = 345"
but can't delete so that there are no duplicate pages. Conundrum!
Did you try to delete it from the trash bin (Remove Deleted Resources) on the line betwen the Resource Tab and the Resources/Documents. When you delete some Resource it's still in the manager and if you want to remove it forever you have to delete it from this trash bin on the right side of the line, below the Resource Tab.
You can see it in the attached file. The screenshot is from MODX version 2.3.3 but it's the same, only the design is changed.