pluggable.php is the built-in Wordpress plugins handler. It looks like one of the plugins he's using isn't compatible with the version of Wordpress that he's using.
I'd have him update Wordpress and all of the plugins first, and if that doesn't fix it, have him disable all of the plugins and re-enable them one-by-one until he finds the culprit.
Then if that doesn't work because Wordpress barfs at the slightest little thing, have him move to something like Squarespace.
Hybrid Mode
