Are the rest of the output files present with the index.htm file? Are you trying to launch the index.htm file from within a zip file?
Index.html does not work if you have published the pptx as AICC course.
Go to adobe presenter>>quiz>>manage>>reporting and check aicc is not selected.
if it is selected, then disable reporting and check again. This time index.html will work.
if this is not the case, Kindly explain in steps what are you trying to do?
if possible, share your pptx with me (mail here: firstname.lastname@example.org , do not share your pptx in forum). .
(Adobe Presenter Engg Team)
Now it works
Thank you very much