If you are stuck on the sixth level this is the guide for you!
How to pass the 6th level?!
Everything on the left seems to be right, but you really need to move the puzzles back and forth where it's just a wall, and in time you will succeed, will fall into place. And you will get the achievement Level 6 and you can continue the game.
The problem area is highlighted in red. That's where you need to move puzzles at random, until it comes out: left and right, etc..
You can also try to repeat the screenshot below, where everything is correct:
That's all, good luck.