here is the full source of an index.php that works. It displays a random image.
`<?php
define('ZENFOLDER', 'zp-core');
define('WEBPATH', 'zenphoto');
require_once(WEBPATH . "/" . ZENFOLDER . "/template-functions.php");
header ('Content-Type: text/html; charset=' . getOption('charset'));
?>
<html>
<head>
<title>Test Index</title>
</head>
<body>
<?php
$randomImage = getRandomImages();
$randomImageURL = getURL($randomImage);
echo "<img src='".
$randomImage->getSizedImage(getOption('image_size')) .
"' alt=\"random image\"n" . $randomImage->getTitle() .
'" />';
?>
</body>
</html>`
This file is in the root folder of the site. Zenphoto is installed in the folder `zenphoto`.
Try it out and see if you get the same result.
Also, please describe the geography of your site. What is the folder structure. Where is zenphoto and where is the "plug-in" use. Where in your plug-in code does the error message occur?