I noticed that is says that greenlighters cannot have profile pictures, so that is the problem. I tried to use the link you have as my profile pic to see if it would work and it did, but only when posted in the 'edit profile picture' page, and not the page that comes up if you were to click on your username link or 'my profile' on the top right of the site.
So once you become a bluelighter (after 50 posts) you can get your profile picture uploaded in the area I linked you to. You can get their manually by clicking 'settings' on the top right of the page, and then 'edit profile picture' which is on the left side of that page under the settings.
The "picture" space you put it in is just for a URL to your picture... That field won't display a picture no matter how many URL tags you throw into it. ;)
To upload an image as your profile picture: Settings > Upload Profile Picture