1st solution located: \Common\Controls\Controls.sln
and its project: \Common\Controls\Common.Controls\Common.Controls.csproj
Description: This is a library that contains this class:

public abstract class OurUserControl : UserControl
{
    // Variables and other getters/setters common to our UserControls
}

2nd solution located: \AControl\AControl.sln
and its project: \AControl\AControl\AControl.csproj
Description: Of the many forms/classes, it will contain this class:

using Common.Controls;

namespace AControl
{
    public partial class AControl : OurUserControl
    {
        // The implementation
    }
}

A note about adding references (not sure if this is relevant):

When I add references (for projects I create), using the names above:
1. I add Common.Controls.csproj to AControl.sln
2. In AControl.sln I turn off the build of Common.Controls.csproj
3. I add the reference to Common.Controls (by project) to AControl.csproj.

This is the (easiest) way I know how to get Debug versions to match Debug References, and Release versions to match Release References.

Now, here is where the issue lies (the 3rd solution/project that actually utilizes the UserControl):

3rd solution located: \MainProj\MainProj.sln
and its project: \MainProj\MainProj\MainProj.csproj
Description: Here's a sample function in one of the classes:

private void TestMethod<T>()
    where T : Common.Controls.OurUserControl, new()
{
    T TheObject = new T();
    TheObject.OneOfTheSetters = something;
    TheObject.AnotherOfTheSetters = something_else;

    // Do stuff with the object
}

We might call this function like so:

private void AnotherMethod()
{
    TestMethod<AControl.AControl>();
}

This builds, runs, and works. No problem. The odd thing is after I close the project/solution and re-open it, I have red squigglies everywhere. I bring up my error list and I see tons of errors (anything that deals with AControl will be noted as an error).

I'll see errors such as:

• The type 'AControl.AControl' cannot be used as type parameter 'T' in the generic type or method 'MainProj.MainClass.TestMethod()'. There is no implicit reference conversion from 'AControl.AControl' to 'Common.Controls.OurUserControl'.

or inside the actual method (the properties located in the abstract class):

• 'AControl.AControl' does not contain a definition for 'OneOfTheSetters' and no extension method 'OneOfTheSetters' accepting a first argument of type 'AControl.AControl' could be found (are you missing a using directive or an assembly reference?)

Meanwhile, I can still build and run the project (then the red squigglies go away until I re-open the project, or close/re-open the file). It seems to me that I might be setting up the projects incorrectly. Thoughts?