SetVec2 works ok..
How to reproduce :
self.shader=Shader:Load("Shaders/Lighting/directionallight.shader")
self.shader:SetVec4("ambientlight",1,1,1,1)
Also tried :
self.shader=Shader:Load("Shaders/Lighting/directionallight.shader")
self.shader:SetVec4("ambientlight",Vec4(1,1,1,1))