Why is skybox pink in build only?

Hi, every time i create a skybox with a custom shader, it will fork fine in both unity editor and testing but when i build the game to android, it becomes pink. There is a custom shader on the skybox though. I have added that shader to graphics

I cant because its after i actually build the game. It works fine in both exitor and player. The shader is also on the object notjing os missing.