Since you mention Internet Explorer, I assume that you are on Windows.
Do you sometimes clear your browser cache? (Tools | Internet Options | tab General | Delete browsing history)
Do you sometimes clear Flash Player local storage? (Control Panel | Flash Player Settings Manager | tab Storage | Delete all)
Does enable/disable Hardware Acceleration make any difference? (See http://forums.adobe.com/thread/891337)
Do you have the latest graphics drivers installed? (See http://forums.adobe.com/thread/945765)
Finally, is your Internet connection stable?