Which is why you need to increase the Z value so that they appear above the boxes.
EDIT: Actually, after looking through that plugin, I don't even see any reason why it would be causing this issue, so I don't think that's related. Your sprites do seem to be behind the boxes though, but unless you literally edited the script to cause this to happen, or installed something that for some reason edits the placement of all of these sprites, there's literally no other reason that would cause this.
EDIT2: Wait, that plugin actually IS the problem, it's just that the issue was stealth fixed without an official update. So you probably installed an older version. Just reinstall a fresh download of that plugin.