It looks like there’s a problem with getting you where you want to go. It could be a couple of things.
You could simply be logged out.
Check the menu bar above. Does that last menu item to the right say Log In or My Account? If it says Log In, click here to log in. Once logged in, you should be good from there.
If you’re already logged in and you still got sent here, then there’s a chance you don’t have access to what you’re trying to see.
If you’re trying to watch a video class, you can get access here.
If all else fails, send David a support email and let him know what’s going on.