there are no usable controls in this group

今天遇到一个怪事, MFC的toolbox是灰的, 不能使用, 后来上网一查找到解决方案:
右键Toolbox, 点击"Choose Items", 重新启动VS2013, 这样toolbox就可以使用了

还有一些解决方案:

1. Closed all instances of VS, went to: C:\Users\Casey\AppData\Local\Microsoft\VisualStudio\10.0, and deleted thesde files:
   toolbox.tbd
   toolbox_reset.tbd
   toolboxIndex.tbd
   toolboxIndex_reset.tbd

2. In VS command promt: devenv.exe/resetsettings

3. In VS: Tools > Choose toolbox Items > .NET Framework Components > Reset

4. In the toolbox tab, right clicked and selected "Reset Toolbox"

5. In the toolbox tab, right clicked and selected "Show All". This shows a long list of tool options, but in every case they are greyed out and not usable.

6. Rebooted

7. Cast a few well chosen hexes and spells at Microsoft