The latest update to the build tool has broken windows setups.
/AppData/Local/.meteor/meteor.bat gets updated to 1.3.4_3 when you run it.
Apparently this starts your app using the old version of the build tool because if you try to run it after that it returns
The system cannot find the path specified.
Changing it back to 1.3.4_1 made it work but of course it updates itself again if I run it