Unable to paint ambient occlusion onto baked model

[ml3m]

I'm trying to fix a model with a mediocre bake (lowpoly from Maya, highpoly from ZBrush) by painting on the ambient occlusion, but I'm unable to do so.

I tried following the instructions on this tutorial, but the message "mesh maps are not paintable" keeps appearing.

This is the model's AO as is right now

[davescm]

You could add an AO channel in Texture set settings then paint on that using a paint layer

Dave

[ml3m]

I've already added AO in the texture settings and it hasn't worked. Though in terms of the paint layer, 

But by a paint layer, do you mean like this?

[davescm]

It looks like you are painting on the basecolor channel. Set your brush material to paint on the AO channel. By default it will be set to multiply so you will need to paint with a darker shade than white for it to show (I am using a value around 0.5 in the example below).

Dave