Occasionally, Adobe Flash may have problems loading videos, or play them slowly, or stop in the middle. This could also apply to other course content.
2.
Regardless of browser type - Adobe Flash cache: Go to http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html, or perform a Google search for Adobe Flash cache. The first panel, Website Storage Settings, is the settings manager for Adobe Flash. On that panel click the Delete All Sites button and ensure the storage setting slider is set to the right for None, indicating it will not cache Flash components. Restart the browser and attempt the lecture once again.