Why did projects stop opening in vs?

Question

C++ / C#

Tried to open some old projects
Now vs says solution incompatible
With all but the newly created ones
What's the matter?
Of the plugins, only resharper is worth it, it seems to have not changed anything. It gives out something like
this:

Unsupported
This version of Visual Studio is unable to open the following projects. The project types may not be installed or this version of Visual Studio may not support them.
For more information on enabling these project types or otherwise migrating your assets, please see the details in the "Migration Report" displayed after clicking OK.
- VTF, "C:\Visual Studio\Projects\VTF\VTF\VTF.vcxproj"
Non-functional changes required
Visual Studio will automatically make non-functional changes to the following projects in order to enable them to open in Visual Studio 2013, Visual Studio 2012, and Visual Studio 2010 SP1. Project behavior will not be impacted.
- VTF, "C:\Visual Studio\Projects\VTF\VTF.sln"

Answer 1

stackoverflow.com/questions/17596543/error-message...

Answer 2

WTF is written through "W".)
My projects are normally updated from 2005 studio to 2015. The problem was only once and I solved it by rolling back to the old project and re-updating.
If there is no old version of the studio on your computer, then the problem could be in the wrong version of the toolset. In theory, the studio itself had to reconfigure it, but you never know ...