omg i just held control in the level editor and it froze up and the thumbnail showed up again. FINNALY for the first time in a year I can make a new level.
That happens to me ALL THE TIME, it happens when you play a level whilst not logged in and when you do log in your browser doesn't notice, and won't allow you to comment. Just close the browser and the problem should be solved.
Just search "snakes" and its the first level.
Its how I learned.