In one of my projects, Visual Studio says it can't find namespace System and similar Microsoft standard assemblies. It also can't load other projects in the other solution that it depends on.

To clarify, it DOES build, but pretty much every line in that project which references another project has a squiggly red "error" underlining.

When loading this solution, or when trying to add a dependency to this project (by right clicking Dependencies and selecting 'Add Reference...', I get this message:

> 
> An element with the same key but a different value already exists.
>  Key: Microsoft.CodeAnalysis.CSharp
> 
> 
> 

The top of the csproj file is:

```
<Project Sdk="Microsoft.NET.Sdk.Web"> 

 <PropertyGroup>
    <TargetFramework>net462</TargetFramework>
    <NoWarn>$(NoWarn)</NoWarn>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
    <TypeScriptCompileBlocked>true</TypeScriptCompileBlocked>
  </PropertyGroup>

```