By default, AD objects are protected from accidental deletion. To remove this protection for all objects in a given scope (i.e. all objects in an organizational unit and below), try this code:
#requires -Version 1 -Modules ActiveDirectory Get-ADObject -Filter * -SearchBase 'OU=TestOU,DC=Vision,DC=local"' | ForEach-Object -Process { Set-ADObject -ProtectedFromAccidentalDeletion $false -Identity $_ }
Note: This code requires the ActiveDirectory module which ships with the free RSAT tools.