Shadow issues on textures

I have a lot of ground textures and for some reason the crease in between these objects/textures shadows appear. Here is an example, part of it is my world and the other is the 3d skybox. http://goo.gl/j3k2Ek
How can I fix this? Also speaking of shadows non of my prop_statics are casting shadows even with a shadow control entity up, everything used to be fine. I am not sure what happened.

Your issue is that you have selected a cube and made all sides of it a displacement. When working with displacements you only select the face you want to manipulate.