The problem is that either the computer is too slow to run the content you're attempting to use, or the content is written inefficiently. The message is presented because the content is causing Flash Player to max out the CPU for excessive amounts of time.
My first recommendation would be to make sure that you have the latest Flash Player running and that the problem page is the only thing running on your computer (close all of your other tabs, programs, etc). If that doesn't help, try other browsers. Flash Player for Chrome, Internet Explorer and Firefox are all different (as are Flash Player for Chrome and Firefox/Safari on Mac), so you may have better luck with one vs. others.
If this is happening primarily when you're watching video, we may not be leveraging your video hardware. This is typically because you either have an old graphics card that's problematic (mostly a handful of really old Intel chipsets), or the drivers are really old and need to be updated. There are instructions on checking hardware acceleration and updating drivers here:
Good luck!