You don't have atmospherics enabled by any chance, do you? Try really large values for the shadow bias, like 5 or 10. What could also work would be increasing the shadow blur - that other dial. And if you haven't done so yet, read Dr. Geeps tutorial about adjusting the shadow lite cams, that can also vastly improve the shadows. (wieder in Englisch damit die stumm mitlesenden auch was davon haben.)