I made the Core Update from 7.17 onto 7.18. I just ran update.php, no errors were thrown.
However when I edit/create one of my content types, I saw the following.

Warning: Invalid argument supplied for foreach() in form_type_checkboxes_value() (line 2288 of ../drupal/includes/form.inc).

I opened a outher ticket. Today, i deactivate content optimizer and the error disappear. So i transfer the problem. The old ticket is closed and a new one is open here.