Problem:
When configuring my Build Service on TFS 2015 I received the following error message when building my SharePoint WSP with the build service.
C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v11.0\SharePointTools\Microsoft.VisualStudio.SharePoint.targets (387, 5) The "ValidatePackage" task failed unexpectedly. System.InvalidOperationException: The project service does not contain the specified project: c7bc030b-17d9-42eb-8dd4-a7c0d3258203. at Microsoft.VisualStudio.SharePoint.Tasks.ValidatePackage.OnCheckParameters() at Microsoft.VisualStudio.SharePoint.Tasks.BuildTask.Execute() at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext()

I have tested a few fixes mentioned on the web as installing Office Developer Tools for Visual Studio 2012* or Open the *.csproj in a text editor and look for the <ProjectTypeGuids> entry and make sure the guids are listed there*.
Nothing worked for me until I figured out a really stupid configuration setting that is quite obvious but I have overlooked.
Resolution:
Our SharePoint 2013 solution was created with Visual Studio 2013 and within the vNext Visual Studio-Build I had configured the Visual Studio-Version 2012. I just needed to set the correct version and it worked like a charm.

*opens an external link in a new tab.