After several failed attempt to follow the manual rule I was able to transfer photos present on the additional SD inserted into the WMD (64G) to the rolling photo of my Ipad following this procedure:
trasfer the photos from SD to the Media Drive Ipload folder
Transfer from the Media Drive Upload to ipad rolling photos
A couple weeks ago, I came across the iOS app “FileBrowser”. This app has all the functionality that the SanDisk app should have, and more. With it, you can create folders on the Media Drive and/or an inserted SD card. You can copy and/or move files from any folder to any other, including moving pics from WMD or SD card to the Camera Roll. You can also connect to most cloud drives with it (OneDrive, DropBox, Box, etc.).
Anyone who has a WMD should get this app (and nPlayer for playing videos).