Exactly what Fugazi said. Too few polys to properly match the calves.  His other suggestions are good too. :)

When I work with dynamic clothes that cause pokethroughs like this, I usually work around in two ways:

1. Import the mesh in Wings and run some smoothing/subdivision on it, if it's really lowpoly, then import it back into Poser and run the simulation. I have a fast computer, so I don't mind the extra calculation, and it will look better. 

2. Work with morphs.  A common case is where there are too few polys around the nipples of V4. If I don't subdivide to accomodate this, I just run the simulation, with the nipples on, and then turn the morph down afterwards. Only problem is to remember to turn it back on..

3. Morph tool. I had a problem with really long faces on a dress I bought that couldn't drape around a character's knee (similar to what you have on the screenshot)  So what I did was to make some morphs on the clothing with the 'pull' tool. gently, subtly.  Then I could use these morphs to adjust the image. 

Morphs and stuff work well if you do still images, but if you're animating, you want to make sure it works fine in every frame. Then subdividing or increasing collision offset a little, or even scaling down the calf in the final animation may be the best idea.