I have a project in Visual Studio with the Language Version set to 'C# latest minor version (latest)' in VS 2017.3 (so this is C# 7.1 - I have also tried setting the version explicitly to C# 7.1).

This builds find in Visual Studio, but in NCrunch I get errors relating to C# 7.1 features such as the one below:

So... this morning I installed an update to VS 15.3.2 and the problem disappeared. The syntax I was using isn't actually a 7.1 feature, the error was a regression (you can see the release notes refer to a C# 7.0 Regression in Tuples).

I've tried pretty hard to reproduce an issue using actual C# 7.1 features, but I haven't had any success. So based on that, I think my original comments can be ignored.