I know there is a question with this same wording, but the solution given is not working for me.
I have a "Venom" head that is modeled and ready to bake out a normal map.
I have tried setting the multires "Preview" to 0 through 5, while keeping "Render" and "Sculpt" at 5. Note, while the multires is set to "not visible" below, I tried with and without visibility enabled.
Regardless, the Normal Map only bakes a blank normal map.