Invalid structure passed to content module on preview

When I preview a existing node, I get the following message:

Invalid argument supplied for foreach() in modules/contrib/cck/content.module on line 636

Trace:

# Time Function Location
1 0.0003 {main}() index.php:0
2 0.4716 menu_execute_active_handler() index.php:15
3 0.5368 call_user_func_array () includes/menu.inc:418
4 0.5368 node_page() includes/menu.inc:0
5 0.5369 node_form() modules/node.module:2125
6 0.5651 drupal_get_form() modules/node.module:1642
7 0.8032 form_builder() includes/form.inc:129
8 0.8543 node_form_add_preview() includes/form.inc:465
9 0.9249 node_preview() modules/node.module:1739
10 0.9415 theme() modules/node.module:1863
11 0.9435 call_user_func_array () includes/theme.inc:166
12 0.9436 theme_node_preview() includes/theme.inc:0
13 0.9436 node_view() modules/node.module:1888
14 0.9436 node_invoke() modules/node.module:545
15 0.9437 content_view() modules/node.module:311
16 0.9502 _content_field_view() modules/contrib/cck/content.module:364