Repro Steps:

1. Open provided projects "TestCubemapArray" scene
2. Enter play mode
3. Look at the console and see that it says that "supportsCubemapArrayTextures True"
4. Select the "SMKSkybox-Cubed" shader in the project view
5. Look at the inspector and see that there's and error

Expected: To not see any errors because Cubemap array textures are supported
Actual: Cubemap array textures aren't supported

Fixed in: 2018.1.0a1

Reproduced with: 2017.1.0b1, 2017.1.0a6, 5.6.0f3, 5.5.3f1, 5.4.0f3

Note:
The user also attached a photo of the console with the error