Hello,
Please make sure you create a HTML5 player by going to KMC->Studio since the Flash player are legacy and are no longer supported.
Once you've done that, if there are still issues, please provide a URL where the player is embedded. You can do that by going to KMC, select an entry and in the "Actions" select box choose "Preview & Embed", in the new screen that will open, you'll see a link under the label "View a standalone page with this player".