Occasionally when you log in, your computer will show you the page that loaded before the login (from temp Internet files on your computer) when you go back to the discussion or other pages. Since you weren't logged in when you were there before, it will look like you're still not.

Of course, it you actually are logged in, you can't do it again.

Click the refresh button at the top of the discussion page, to make your computer reload a fresh copy. You may see that you actually are logged in.

In IE, there's also a "Refresh" icon on the top toolbar.

John