My guess is that they are being blocked by the proxy. The only other thing that I can think of is to make sure you have the latest version of flash player installed. If it's not Flash or the proxy, then there is likely a setting on your computer or browser that may be causing the issue, but I can't say for sure. I don't want to tell you to change any of those settings, especially if it's a work computer.
An alternative is that you can go to our youtube channel and view the videos there since youtube isn't blocked: www.youtube.com/user/sparkpeople
Hope that helps!
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford