Problem with assembly references in Visual Studio

I created a new project in visual studio proj2, and I want it to have the same build links as proj1, so I opened proj1.csproj and copied:

<ItemGroup>
<Reference Include="mscorlib" />
<Reference Include="system" />
<Reference Include="System.Windows" />
<Reference Include="System.Core" />
<Reference Include="System.Xml" />
<Reference Include="System.Net" />
<Reference Include="System.Windows.Browser" />
</ItemGroup>

and paste it into proj1.csproj. The problem is that my reference to the System.Windows assembly has an exclamation mark next to it, and when I try to click it, it says:

This project cannot be viewed in Object Explorer because it is not available or has not yet been created. Make sure the project is accessible and built.

And of course, in my .cs file it says

The type or namespace "Windows" does not exist in the namespace "System" (do you miss the assembly reference?)

How do I get assembly links?

+5
5

, Framework 3.0.

+7

System.Windows - WPF, , ,.NET 3.0.

+2

, . , .NET 4 System.Windows...

, System.Windows.dll System.Windows; Presentation*.dll. , , , , .

.cs, ; , , , , .

+2

, , Framework, . proj2 , proj1.

, Visual Studio, "" " " "".

.csproj , TargetFrameworkVersion. ProperyGroup .

+2

" ".

System.Windows.

0

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