Sometimes when I try to access a video, I get a message like this: "To view this site, you need to have Flash Player 9 or later installed. Click here to get the latest Flash player." I have Flash Player 10.1 already installed and it seems to generally work. I've tried uninstalling and reinstalling, with no success. This only seems to happen on certain sites, like www.pbs.org. How can I get these sites to work?