There are some differences in v1.2.x vs 1.3 related to loading the define-pages content. If you haven't upgraded the pairs of files to the new structure, you'll get the indicated error.
includes/modules/pages/index/header_php.php
v1.2.x:
PHP Code:
$define_main_page = zen_get_file_directory(DIR_WS_LANGUAGES . $_SESSION['language'] . '/html_includes/', FILENAME_DEFINE_MAIN_PAGE, 'false');
v1.3:
PHP Code:
$define_page = zen_get_file_directory(DIR_WS_LANGUAGES . $_SESSION['language'] . '/html_includes/', FILENAME_DEFINE_MAIN_PAGE, 'false');
includes/templates/YOURTEMPLATE/templates/tpl_index_default.php
v1.2.x:
PHP Code:
<td class="plainBox"><?php require($define_main_page); ?><br /></td>
v1.3:
PHP Code:
<div id="indexDefaultMainContent" class="content"><?php require($define_page); ?></div>