v11.0\WebApplications\Microsoft.WebApplication.targets was not found when file actually references v10
First some background. At the end of 2012 we migrated our vs2008 solution to vs2010 but we still target .NET 3.5. (I know nothing but the latest and greatest here!)
We hadn't had any issues with this setup until a few weeks ago when people started getting these errors:
"foo.csproj" (Rebuild target) (16:5) ->
C:\...\foo.csproj(142,3): error MSB4019: The imported project "C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v11.0\WebApplications\Microsoft.WebApplication.targets" was not found. Confirm that the path in the declaration is correct, and that the file exists on disk.
The interesting thing is that if you look at the project file it references v10 which makes sense because we don't use Visual Studio 2012.
This error hit several of us at once and even on older code branches that haven't changed in months.
I suspect some update got pushed onto our machines that confused things but I don't know what to do about it.
The short term solution has been to install VS 2012 and not use it but I'm hoping for something a little cleaner than that.
Answer
I ran into the same issue with Visual Studio 2013. It turns out that I was using the old version of MSBuild--the one that ships with the .NET Framework--from the command line. Microsoft is now releasing MSBuild as part of Visual Studio itself and also as a separate installer (http://blogs.msdn.com/b/visualstudio/archive/2013/07/24/msbuild-is-now-part-of-visual-studio.aspx).
The solution was to use the new version of MSBuild.exe located in C:\Program Files (x86)\MSBuild\12.0\Bin. Once I did that, all the targets errors disappeared.
EDIT 1
As mentioned in the comments, each new version of MSBuild brings with it a new directory. For Visual Studio 2015, use C:\Program Files (x86)\MSBuild\14.0\Bin.
EDIT 2
As mentioned in the comments, for Visual Studio 2017, use C:\Program Files (x86)\Microsoft Visual Studio\2017\<Edition>\MSBuild\15.0\Bin\MSBuild.exe.