--- Operating System, Graphics card ---
os: windows7 64bit
GPU: NVIDIA Quadro K4000

--- Blender version with error, and version that worked ---
2.68RC1 (r57908)

--- Short description of error ---
when rendering te viewport with Gather> Raytrace> Sampling> Constant Jittered enabled then blender crashes

--- Steps for others to reproduce the error (preferably based on attached .blend file) ---

1. switch to viewport Shading > Rendered
2. enable Ambient Occlusion in the World Tab
3. in the Gather panel change the samplin gmethod to "Constant Jittered"
4. make the viewport render to trigger a render and blender will crash