When using Automatic SEO Links, putting a slash "/" in the text to look for can result in thousands of PHP Warning: preg_match_all(): Unknown modifier in automatic-seo-links.php. The unknown modifier will be the letter after the slash (i.e. you won't see a warning if the letter following the slash happens to be 'x').
Hack to fix: add this after foreach($links as $link){ on line 569:
$link->text = preg_replace('/\//','\/',$link->text);
(Using Automatic SEO Links 1.41; 64-bit PHP 5.2.5)