TeamCity + ASP.NET Webapp: Error about unclosed string literal?

I have a solution where all projects are targeting .NET v4.5.1.

TeamCity (v9.0.4) previously has built the solution just fine.

Added an Asp.Net web application (MVC + WebAPI) to the solution, still targeted at .NET 4.5.1.

It Works on My Machine^tm, but TeamCity now fails the build with the following MSBuild error:

[src\app\Web\Web.csproj] C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v12.0\Web\Microsoft.Web.Publishing.targets(186, 67): error MSB4025: The project file could not be loaded. There is an unclosed literal string. Line 186, position 67.

Those might be the line numbers in the targets file that threw the error, because in my file all I see is a </ProjectReference> (which corresponds correctly to two project references that are there.

Any idea what could be causing this?