On Windows Vista and newer Windows Explorer runs with medium integrity level.
If you run Visual Studio as administrator (high integrity level) then for security reasons OS will disable drag and drop from Explorer to Visual Studio.
You can either run Visual Studio as normal user or you can install VSCommands for Visual Studio 2012 extension. It has several features that can help with this such as:
- Elevated Windows Explorer – small tool which looks like Windows Explorer but runs with elevated permissions allowing Drag And Drop
- Directory Explorer – tool window inside Visual Studio which again looks like Windows Explorer and allows Drag And Drop
- Run Visual Studio with medium integrity – allows Drag And Drop from Windows Explorer, but you won’t be able to attach to processes run by other users (e.g. IIS)