That's interesting - the tile that contains the trunk, that they're walking onto, is set as a star, which means the program should look at the tile underneath - the cliff - to determine the passage setting. It's not, so that makes me think you've also drawn on that spot with another tile - possibly a blank tile that you thought might erase something you put there but didn't want, and that tile has an O passage setting.
The ONLY tile you should use to erase is the top left B tile. Could you please check again to make sure the top left B tile has a star as passage setting, then use that tile to draw over that spot on the map - it will erase the tree trunk tile. Then grab the tree trunk tile and draw it in again. This will remove any "invisible" tiles with O passage setting and make sure it's JUST your tree trunk that's there.
If you get that problem resolved though, you WILL have the same issue on the tile below where they start - because you've drawn with the shadow there, and the shadow has O, they will be able to walk onto the cliff from the tile above or the tile to the right.
The solution is to either not put passable tiles so close to cliff edges, so it doesn't override the cliff's passage settings, or to put another impassable tile there as well to block access.
