A couple of changes to the build system (which speeds up the compile time) may cause problems for windows users. The error message is something like “missing future”. The solution is to use pip to install “future” and “lxml” and then it all starts working.
Hopefully we can update the Windows Toolchain installer to add these new requirements. Until then, I’ve created an issue here:
https://github.com/ArduPilot/ardupilot/issues/4966
-Randy