Javascript not working on Windows IIS server site

I am experiencing trouble with what should be a very simple .js script on a website hosted on Windows server 2003 / IIS 6.  I have script called lightbox.js (from http://www.huddletogether.com/projects/lightbox/) which works perfectly on one site on the same server. I am simply copying everything from the working site and cloning it on a development site. All the code, directory structure - everything is the same on the second site. The problem I have is that the script is simply not operating. There are no errors or warnings - simply nothing from the script at all.

I have exhausted all other avenues to try and resolve the issue and my only remaining thought is that somehow Javascript needs enabling on a site-by-site basis on the server. I've not experienced this before - I've only ever known Javascript to work across all sites on a server. Does anyone know if it's necessary to enable script operation on a site-by-site basis in IIS? And if so, how?