It's difficult at best combining Lightbox's Prototype/Scriptaculous script libraries with Animated Collapsible's jQuery script libraries. Even when successful, it's a duplication of sorts resulting in far more code than is neccesary. They both do the same sorts of things, just differently.
I'd recommend using jQuery based SlimBox 2 instead of Lightbox. It's a drop in replacement:
Install it's script and styles in the head of the page instead of Lightbox. You may leave the rel="lightbox[garden]" and any other Lightbox type links 'as is'. The script will pick up on them.
With SlimBox/Collapsible you only need one copy of jQuery for the page. The external tag to jQuery should come before the ones for both SlimBox and Animated Collapsible.
However, I'd suggest updating jQuery from: