You are probably using Internet Explorer or Safari as your preferred browser?
Easiest solution here is to use a browser that doesn't require Flash. Google Chrome and Firefox work without Flash plugin and video quality is better.
If it is not possible to switch to another browser, instructions to fix the Flash problem are below:
This error messages indicates that your Flash Player's cache is full.
This problem is easy to fix. Go to Global Storage Settings page, uncheck the box "Store common Flash components to reduce download times" and choose "confirm".
Then check the same box again (yes, the very same one you just unchecked). This clears Flash Player's cache, and should solve the problem.
You can also use Google Chrome, which uses HTML5 and not Flash Player. You can download Google Chrome from the link below: