Any reason why this plugin should fail on a Zeus server

I have this plugin working perfectly on a test site running Apache.
I’ve migrated the plugin and all the settings to a site running Zeus, and the plugin no longer works. No errors are generated, but no news feed items are shown – just ‘undefined’. News feed url is identical in both cases.

http://wordpress.org/extend/plugins/fade-in-fade-out-xml-rss-feed/