I am trying to target .NET 4.6 and also take advantage of the latest C# version by changing the C# language version to 6.

However during compilation I got this error:

&gt; Error Invalid option &#39;6&#39; for /langversion; must be ISO-1, ISO-2, 3, 4, 5 or Default

If I update the `/langversion:6` in Web.Config setting to 5 it works,

      &lt;system.codedom&gt;
        &lt;compilers&gt;
          &lt;compiler language=&quot;c#;cs;csharp&quot; extension=&quot;.cs&quot; type=&quot;Microsoft.CSharp.CSharpCodeProvider, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089&quot; warningLevel=&quot;4&quot; compilerOptions=&quot;/langversion:6 /nowarn:1659;1699;1701&quot;&gt;

But how do I resolve this without resorting to lower language version?

I am using Visual Studio 2015 Community Edition, and I have also installed .NET Framework 4.6 manually just in case it was not installed by default by Visual Studio 2015.

The project is a standard ASP.NET MVC template project created by Visual Studio 2015.


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Error Invalid option '6' for /langversion; must be ISO-1, ISO-2, 3, 4, 5 or Default