Just subscribed to substance and found that the same error is happening when I import some substance file from the substance source itself !
Paid $ to subscribe, download thinking I can use it in Unity, but no.. not possible. And there were no sign of compatibility anywhere for Unity integration that I could find.
Using Unity 5.6
When we will be able to get some full compatibility ! ? ! 
V6 engine support was added in the Unity 2017.2 beta builds. Any older Unity version with a substance using the V6 engine nodes (text, curve, etc) will give an error when being imported. Unfortunately, there are currently no plans to backport these fixes to older Unity builds.
Are you using Substance Designer 2017.1.3? It is defaulted to the Substance Engine v6. Therefore, there can be some compatibility issues if the sbsar is exported from there without changing the compatibility mode to Substance Engine v5.
You can do this by going to Edit -> Preferences -> Projects and clicking the Compatibility Mode dropdown.

It will then highlight nodes in your graph in yellow that must be removed or changed to be able to be exported correctly and work with Unity 5.6.

If you have any further questions about this, let me know.
