The problem occurs when you preview a course after publishing. You see the black screen when you click the index.html file. In this case, the file is launched from the file server and cannot display as expected.
Launch the course from the web server. Make sure that you copy the file on the web server and then fetch the course from the web server.
When previewing the course from within Captivate, this task is done automatically by Captivate by setting up the web server on your localhost.