raspberryjamcloth, this file (the Cherry Zen fixed one) was written for v1.4 of Zen Lightbox. It will not work correctly with v1.5.

A quick fix would be to find the following code in this file...

Code:
rel="lightbox[gallery]"
and replace it with...

Code:
rel="lightbox-g"
This should work, but I don't use the Cherry Zen template so cannot confirm this.

I've added this issue to my todo list and v1.6 will include an up-to-date fix for the Cherry Zen template.

I hope the above fix works. Please let me know how you get on.