This happens when the properties panel is pinned to the material tab.
Traceback (most recent call last):
File "/home/ralf/Source/blender/build/bin/2.76/scripts/addons/cycles/ui.py", line 613, in draw
is_sortable = len(ob.material_slots) > 1
AttributeError: 'NoneType' object has no attribute 'material_slots'
location: <unknown location>:-1Fixed by moving the material_slots access after the object context check.
Steps to reproduce
- open
- check the console output