Why do I keep getting: Error ('=' expected near 'is')? I don't even have the word 'is' in my script.

local sides = 6
local radius = 4
for i=1,sides do
local s = math.tan(math.rad(180/sides))*radius
print(s)
side = Instance.new("Part")
side.Material = "DiamondPlate"
side.Parent = game.Players.LocalPlayer.Character.Head
side.Anchored = true
side.Size = Vector3.new(.1,.1,2*s)
side.TopSurface = "Smooth"
side.BottomSurface = "Smooth"
side.BrickColor = BrickColor.Yellow()
side.CFrame = side.Parent.CFrame * CFrame.new(0,2,0) * CFrame.Angles(0,math.rad(360/sides*i),0) * CFrame.new(radius,0,0)
end

why does it keep giving me this error? ('=' expected near 'is')

First of all, use the code block. No one can understands your thing. Second, why are you trying to run it on the script builder? Script builders has limited access not UNLIMITED.
Third, at the output, where is the error located at? Is it coming from your script or other scripts?