Invalid argument in fold_pages plugin

I use the following code for displaying three levels of pages:
‘

<!– Top level navigation –>
<?php wswwpx_fold_page_list (‘depth=1&&exclude=11,12&sort_column=menu_order&title_li=’); ?>

<!– Sub level navigation –>
<?php
$g_page_id = $wp_query->get_queried_object_id();
$ancestorIDs = _wswwpx_page_get_ancestor_ids($g_page_id);
$grandParent = $ancestorIDs[1]; ?>
<ul id=”submenu”>
<?php wswwpx_fold_page_list(“title_li=&depth=1&sort_column=menu_order&child_of=”.$grandParent); ?>

<!– SubSub level navigation –>
<?php
$SubgrandParent = $ancestorIDs[2]; ?>
<ul id=”subsubmenu”>
<?php wswwpx_fold_page_list(“title_li=&depth=1&sort_column=menu_order&child_of=”.$SubgrandParent); ?>
‘

But, when on the top level navigation, I get the following error:
Warning: Invalid argument supplied for foreach() in …/fold_page_list.php on line 359

Anyone who can help me out here?