Open the project.

Observe the two pink spheres

The sahders on these spheres try and use custom lightmap functions including the optional viewDIr. For some reason they error out with
'expression left of ."viewDir" is not a struct or array'

The original thread can be found here, and where Aras has requested this be submitted as a bug.

http://forum.unity3d.com/threads/custom-lightmapping-viewdir-seems-to-be-broken.251393/

According to this page using an optional ViewDir in the custom lightmap function paramaters should work (decode lightmaps)
http://docs.unity3d.com/Manual/SL-SurfaceShaderLighting.html

The ToneMapLightmap shader in the supplied project uses the shader found here
http://docs.unity3d.com/Manual/SL-SurfaceShaderLightingExamples.html

which works, but once you add viewDir to it fails.