Sometimes when you use a whole lot of Painted Shaders with lots of strokes, it can cause an issue like this. Unfortunately the only solution currently is to go in and edit the TGD and remove the Painted Shader stroke data. We're looking into the cause of this, of course. In the meantime if you have a *lot* of stroke-type masking to do, it's better to do it with imported image masks. The Painted Shader is still quite useful for smaller, quick internal paint-type control.
- Oshyan