Well nobody here can see the obstruction that's causing your top tray to get stuck - but you should be able to see it.
Take the tray off the runners and try each runner in turn without the tray fitted - if the runners work without binding then you may have an issue with the tray itself.
This is a problem that requires careful observation leading to a conclusion and resolution - this is the way to get it fixed.
Good luck with the looking & thinking..., April 2015
