File "/Users/aled/Library/Application Support/Blender/2.79/scripts/addons/rprblender/core/nodes.py", line 984, in get_sss_radius
val = blender_node.inputs[getattr(blender_node, input_id)].default_value
KeyError: 'bpy_prop_collection[key]: key "Subsurface Radius" not found'
1. Loaded Blender from terminal by typing "blender".
2. Opened an existing Blender file created with an older version of RPR.
3. Press preview render. Get ERROR reported on the render view.
4. Look in log (see above for log).
5. Hint is Subsurface Radius not found.
6. Open a Material with an old Uber.
7. Place a new Uber next to it and turn on the same items.
8. See that Subsurface Radius is indeed not on the old Uber.
9. Have to reconnect and re-setup the Uber shader to work again.
Loading older files should add at least basic defaults on existing Uber shaders (and all the others that change from version to version).