Rotobrush CS6 Problem

Here's my situation. I've got a 3 second shot of a woman's mouth talking that I've rotoscoped out just the lips. Rotoed at full quality, everything looks great. BUT there is ONE FRAME that rotobrush is not responding to. When I paint an area on the lips I get nothing. No sort of radius at all. Very perplexing. I have no clue on this one. I tried increasing and decreasing the search radius, changing the size of the brush, still nothing. The mouth is closed on this frame btw. I need help on this ASAP! Thanks!


Clarke