I ran into this problem when trying to setup a dev site. I have an SVN repository from which I push onto the live site, and I have a separate development site on my local machine. Since I only had changes to the PHP files that interested me, I set up my local machine to use (share) the remote/live DB. The first time I tried to run zenphoto on my local machine I got the missing script error, since it turned out `getOption('zenphoto_install')` and `installSignature()` obviously didn't match, since the install sig is made using $_SERVER['SERVER_ADMIN'] and $_SERVER['DOCUMENT_ROOT']....... but I guess this would also affect you whenever you moved servers. I guess you can just manually print out your installSignature and reset it in the DB if it's a permanent move.
http://php.net/manual/en/reserved.variables.server.php
It's definitely something that stops you from simply being able to move / duplicate your entire ZenPhoto install w/o tracking down how the installSignature works.... not quite sure if that's a bug or a feature