Possible Reasons:
 Web Server not running
 URL incorrect
 Project not published
Web server hosting wrong folder

Solution:
Verify Web Server is running and hosting the correct folder
 Make certain project is published
 Verify URL

If above is not the reason, you need to verify that Web Client configuration is done properly.
You can refer  below Video:
https://www.youtube.com/watch?v=mc07e9gZag0

Released for:Schneider Electric India