Can't add an existing folder to Visual Studio 2012. "Include in Project" menu option is missing

I am running Visual Studio 2012 (administrator) in Windows 8. I am unable to add an existing folder using Solution Explorer. I also can't drag the folder from File Explorer into the Solution Explorer. I get the invalid target drop icon.

The only way I know is to add the folders by Add - "New Folder" and creating the folders manually.

Why am I am having these issues?

Why is 'Include in Project' menu option missing?

How do I add folders to project solution in Visual Studio?

Open your project in Visual Studio > click the Show All Files button > expand the bin , Debug > select and right-click the parent folder > choose Include in Project option.

How do I add an existing project to Visual Studio?

In Solution Explorer, select the solution. On the File menu, point to Add, and click Existing Project. In the Add Existing Project dialog box, locate the project you want to add, select the project file, and then click Open. The project is added to the selected solution.

Click the icon for "show all files" in Solution Explorer. You will then be able to see any pre-existing directories and include them in your project.