Cannot run in Visual Studio but works in VS Code

I have a project that runs fine in Visual Studio Code, but won't run in Visual Studio 2017. When I run the project, I get a console window that pops up briefly reading:

unhandled exception: system.io.filenotfound exception: Could not load file or assembly 'Microsoft.AspNetCore.Hosting.Abstractions, Version=2.0.2.0....' or one of its dependencies. The system cannot find the file specified. Main(String[] args)

The following is in the output window:

The program '[18664] project.dll' has exited with code -532462766 (0xe0434352). The program '[18664] project.dll: Program Trace' has exited with code 0 (0x0).

The program runs fine in Visual Studio Code.

My solution consists of two projects:

My startup project is has the following SDK dependencies: - .NETCoreApp2.0 - .NETStandard2.0

My secondary project targets NETStandard.Libary v1.6.1