When opening any sample code of CRM 2015 in Visual Studio 2013 we usually get an error to install .Net Framework 4.5.2 and projects don’t get loaded.
Even after installing this error will not go away.
To fix this issue simply download .net framework 4.5.2 developer pack and install it
After installing this, try opening a project/solution again and all project will get loaded with out any issues
link to download developer pack