I think I worked it out. It was one of the first puzzles I made so it's not 100% perfect. It only works if you push the boulder in front of it on to the blue button. I think you might have pushed that boulder away and pushed another boulder on to it. Totally my mistake and is something I will fix. Again sorry about that. (and well done you for finding that bug!)
But the good news is you are both nearly free!!!