Thanks, I read that and successfully fixed the problem. I am unsure as to the original cause, however a query to the web hosting company returned this info:
"The problem may due to PHP5.3 that has been installed to GAME server on 2012-08-20. It is possible that your script is not compatible with PHP5.3. You can try to change PHP version for your account back to PHP5.2 by add the following code to your .htaccess :
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AddHandler application/x-httpd-php52 .php
Could the change in PHP versions be responsible for my original problem?
I didn't change the .htaccess file, as the site is now working once more. When I ran the setup again, it came back with a list of files that ZP reported as "changed", which included all of my custom pages, along with some other files. I checked the timestamps on all of them, and all were from the same date of about a month ago.