I’m running into a similar issue. I have published Captivate Sims (to HTML5) that I embed using the Web Window. I used to be able to preview these in RUN mode on a Win 7 system. I recently upgraded to Win 10 and now cannot preview them in RUN mode. It does work, as you stated, when published or viewed in a web browser. So, I’m thinking that something changed with Windows, but I’m not sure. I contacted Trivantis support, but no answer at this time.