NuGet.Configuration.ISettings issue in Visual Studio 2015

Hello Friends,

in visual studio 2015, while I am trying to create new project or, build an existing project or click on "Tools => NuGet Package Manager => Package Manager Console" I got bellow errors.

 

 

& When I clicked ok, I got

 

 

then I repaired my visual studio & again I tried But same thing happened. Then i

re-installed visual studio 2015. Then I got bellow message 

 

I tried a lot but can't solve the issue. need your help.