Error: Mixed-mode debugging for x64 processes is supported only when using Microsoft .NET Framework 4 or greater
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
To debug mixed native and managed code in a 64-bit process, you must have .NET Framework version 4. Mixed-mode debugging of 64-bit processes with .NET Framework versions earlier than 4 is not supported.
To correct this error
Perform one of the following steps:
Upgrade your .NET Framework to version 4.
Build a 32-bit version of your application for debugging.