[draygin]

The back side of the cliffs. I think the problem is you dont have it lining up right. Try moving the straight side of the back cliff over left or right one tiles.
Covering 1 tile width of the back tile. Then copy and paste it onto the end of it so its still the same length. I'll try to use a little diagram since I cant show you since I'm at work.

back side of the wall there are two tiles that make up the back row. Move them over like so..
1212121212
/ .................... \ <How you have it.

2121212121
/................... \ <How you should have it.

Get what I mean? Its a matter of the back row not being lined up properly. (I think) So its making it look like tile errors.