Looking at the project file, my first guess is that the relative path to the
"System.Data.SQLite.Core.targets" file is a problem.  Relative paths typically
are based on the current directory, which may not be well-defined when building
within the IDE.  It's certainly possible that my guess is wrong.  The Visual
Studio team may know more about why this setup suddenly stopped working.  Perhaps
there is some third-party plugin or tool that is changing the current directory
during the build process?