I'm using Poser 11 with the Comic Book Preview. Most of the time, the shadows on my actual figures come out very nice, but right now I've put a light behind a figure and am casting his shadow on the floor -- and as you can see in the inset -- it is very jagged along the curves. There is only one light in this scene: Infinite with a shadow map size of 4096. Likewise, I've set the Preview Resolution to 8192 (and higher), but nothing helps or even effects the outcome. Shadow blur did soften the edges, but that's not the effect I'm looking for. I've also experimented with renders from 1,000px thru 10,000px -- although the jaggies are smaller when rendered at 1,000px, they're still there. I've also played with Shadow Samples, Shadow Min. Bias, and so on. Nothing seems to help.

Any suggestions on how to clean this up?

I've attached a sample and screenshots of my light settings.

My System for this job: ASUS Essentio Desktop: Windows 10 Home, 16GB DDR3 RAM | Intel Pentium E5500 Dual Core @ 2.80GHz | GeForce GTX 960 (EVGA) 4GB (04G-P4-3962-KR) 1024 CUDA Cores

Since your render is raster rather than vector there does tend to be a jaggie or pixelated edge based on your resolution. In your render drop down menu you can choose antialias document. This should reduce the "jaggies" when you render in preview mode. It works for me fairly well.