Let’s fix this problem by changing admin/lib-banner.inc.php. Replace http:// with https:// at line 21:
$buffer .= “codebase=’https://fpdownload.adobe.com/pub/shockwave/cabs/flash/”;
After this little modification warning will be gone.
Openads caches banner’s html template, so changes will affect new banners only. You’ll have to re-upload your old banners for this to work!