Hi,
This seems to only happen on a fresh launch of Corona, but when setting the path for HTML5 export the “Build” button stays disabled until you restart.
I’ve tried to demonstrate the issue in this video. If you have any other questions, let me know.
https://www.youtube.com/watch?v=EU-18w1HNN0
Make sure to set the quality to 720HD if watching full screen.
-dev