Using VS Community 2015 and created a default web MVC app that works fine locally but Appharbor gave this error on build
error ASPRUNTIME: Could not find a part of the path 'D:\temp\vr4kg55i.jlt\output_PublishedWebsites\TestAppharbor\bin\roslyn\csc.exe'.
Is AppHarbor ready for the latest .NET app?
I was having the same problem and here is what I found: appharbor support.
As suggested, adding this to the end of the web prject .csproj file, fixed the error:
...
<PropertyGroup>
<PostBuildEvent>
if not exist "$(WebProjectOutputDir)\bin\Roslyn" md "$(WebProjectOutputDir)\bin\Roslyn"
start /MIN xcopy /s /y /R "$(OutDir)roslyn\*.*" "$(WebProjectOutputDir)\bin\Roslyn"
</PostBuildEvent>
</PropertyGroup>