VS2015 Nuget error but not using Nuget at all

Yesterday i upgraded from visual studio 2010 to vs2015. I have an existing project, a simple Windows Forms application that used to build without problem. Now when building the project in VS2015 i get Error while restoring Nuget packages, HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY).

I'm not using Nuget, don't know what Nuget is, have no nuget package folder in my project, so don't have the slightest idea what goes wrong.

Searched a lot for solutions but they all seem to refer to problems using packages, not to problems with not using packages.

Can anyone help me out?