**System Information**
Operating system and graphics card
windows 7 cuda 5.5 driver nvidia 320.57 nvidia gtx 560
**Blender Version**
Broken: Blender 2.69 r20131120
Worked: Blender 2.69 r61240
**Short description of error**
When I work in cycles "Viewport shaiding" bledner crash radomly when I fast clik,change settings in enviroment, textures cycels .
I like work fast and this big problem.
**Exact steps for others to reproduce the error**
Based on a (as simple as possible) attached .blend file with minimum amount of steps
{F29741}
{F29743}