This fix is for if you are facing an error in VSTS agent build: MsBuild.exe does not exist at '/Library/Frameworks/Mono.framework/Versions/4.6.1/lib/mono/4.5/msbuild.exe'.
This is a known NuGet bug ( https://github.com/NuGet/Home/issues/3085) and the fix is in the in 3.5-rtm release
Please reference the following screenshot and use the custom NuGet.exe located at "/Library/Frameworks/Mono.framework/Versions/4.6.1/lib/mono/nuget/NuGet.exe"
(Courtesy of Madhuri from Microsoft and Joe from Xamarin. Source: https://github.com/Microsoft/vsts-tasks/issues/2828)
Please contact our support staff if you have more questions.