First I would check if your MusicKarma project has Microsoft.Net.Compilers in its packages.config file. If not then you could remove everything to do with that NuGet package from your MusicKarma.csproj.
If you are using the Microsoft.Net.Compilers NuGet package then my guess is that the path is incorrect. Looking at the directory name in the error message I would guess that the MusicKarma solution file (.sln) is in the same directory as the MusicKarma.csproj. If so then the packages directory is probably wrong since by default the packages directory would be inside the solution directory. So I am assuming that your packages directory is:
C:\Users\Bryan\Documents\Visual Studio 2015\Projects\MusicKarma\packages
Whilst your MusicKarma.csproj file is looking for the props file in:
C:\Users\Bryan\Documents\Visual Studio 2015\Projects\packages\Microsoft.Net.Compilers.1.1.1\build
So if that is the case then you can fix the problem by editing the path in your MusicKarma.csproj file or by reinstalling the NuGet package.