The game crashes when i do the command /setblock <x,y,z> observer 6

My friend showed me a really cool redstone machine that moves. so i made a world where two of them could race so a used command blocks to create it then when i did "/setblock <x,y,z> observer 6" Then the game crashed. so i went back in the world to see what went wrong. i tried changing the poison of the observer the game didn't crash. so then i tried doing it in another world and the game crash. then i tried putting a piston in poison 6 and the game didn't crash.