When I right click on the Visual Studio 2012 Toolbox and select Choose Items..., the Choose Toolbox Items dialog doesn't show up.
The behavior is:
The text "Loading 'Choose Toolbox Items' dialog..." will display on the status bar, and will remain there until the focus get lost from the screen, by either clicking another window in Visual Studio, or by clicking a different application in Windows.
I performed a Visual Studio repair from Programs and Features, and that didn't help.
I also ran Visual Studio 2012 as an Administrator and that didn't help either.
In the past I installed Visual Studio 2012 Beta, and currently I have installed the Professional Version, with Update 1 on it.
When I right click on a .sln file in Windows Explorer, and select Open With from the menu, the option to open the solution in Visual Studio 2012 is shown as Microsoft Visual Studio 11 Beta.