If you are moving towards the teleporter stone when you click on it, you are standing too far away when trying to drag and drop it into your inventory. If you can not get close enough to pick it up, put the teleporter stone you have in a chest and download (or get from a previous save) a new set.
Lost Items - guide and directory of inventory files

You might also be able to drop the other telepoter stone, move into the wall (or whatever), pick up the stuck one, and use it to teleport out.
Teleporting Anywhere, via hex editor