I get an error when I try to attach a shader to the game. the error is ""float4" undiclared identifier". Why so? did I forget to include anything in my script? I have only default.c and acknex.h

Please read the manual about shaders. You can't include them into your Lite-C scripts, but you assign them to a material instead.

OK. it's just a matter of rephrasing, I assign them to a material. The effect itself is in the "name.fx" file. But when the engine tries to read the file, this error occurs.