Chances are you are actually throwing Javascript errors, if you check your error console, as I'm experiencing the same behavior after uninstalling 1.4 and installing 1.5.
I'm seeing the following errors in the console:
Code:
$.element is not a function in zen_lightbox_mootools_custom.js
This occurs on page load. When clicking the actual image, I receive the following:
Code:
Hash.each is not a function in zen_lightbox_mootools_custom.js
I'm not sure if this is something residual from my previous install (which I had to eliminate due to the IE 7 error), or something is misconfigured on my new install.