If it's a dynamic dress you've probably backfacing polygons intersecting the surface of the dress (the supposed visible surface) try to smooth the parameters , collision offset and collision depth . If you want this result (your picture) the solution is also simpler: make two render, one like this and the other one with backfacing poly turned off, then put them on two layers and use the second one to correct the wrong part of the first one
P.S. You can even make another render with only the dress, one shoulder of
Posette intersects the dress, in that way, you can use the "only dress" render to correct everything.