Had this strange popup trying to remove an old Exchange user and it referenced a CN=iPhone in the error. I assume its something Exchange created for the iphone, but here is how I got rid of it:

  1. Fire up ASDIEdit.msc and open the default naming context
  2. Drill down to where the user is stored in AD and you’ll find a container underneath the user
  3. Right-click on the item in the folder and go to Properties
  4. Take ownership of the object, reopen and then you can give “Authenticated Users” full access to it (since we’re deleting)
  5. Now you should be able to able to delete the user