In my case, this was caused by a subclass name being used in the very next line as a variable name with a different type:
var binGlow: pipGlow = pipGlow(style: "Bin")
var pipGlow: PipGlowSprite = PipGlowSprite()
Notice that in line 1, pipGlow is the name of the subclass (of SKShapeNode), but in line two, I was using pipGlow as a variable name. This was not only bad coding style, but apparently an outright no-no as well! Once I change the second line to:
var binGlow: pipGlow = pipGlow(style: "Bin")
var pipGlowSprite: PipGlowSprite = PipGlowSprite()
I no longer received the error. I hope this helps someone!