I see this message at the top of a newly loaded page:

Warning: Invalid argument supplied for foreach() in [path]/includes/functions_post_thanks.php on line 222
And it's duplicated below itself several times.

Also sometimes when I try to view a page I get this message:

Unable to add cookies, header already sent.
File: /home/concept/public_html/forums/includes/class_core.php
Line: 3338
And when that appears I can't view the page at all.