I would recommend installing Image Handler 2.

See if that helps.

Also, when the lightbox appears on your site it is displayed under the flash banner (at the top). To work round this simply place your flash code (in your header file) inside the following tag...

Code:
<div class="flash"> your-flash-code-goes-here </div>
Also make sure that the class flash doesn't exist in any of your css files.

This will basically tell Zen Lightbox to hide any elements with the 'flash' class.

Hope this helps! :)