LOL You would think so, huh?
Found what it was. Another Boof-inator blunder, as hard as you might find that to believe. (You ARE allowed to act surprised and blame it on vBulletin. In fact, it is encouraged at this point.)
It seems that hook doesn't like this very well:
Code:
$userinfo['action'] = '<i>Donating to Fathers' Rights Forums</i>';
Back slashes are our friends.
What threw me off is that hack that is for wasn't even showing as having anyone on that page and it was sporadically giving the error. I don't understand why it wasn't either an all-time thing or just when they hack was in play. But it showed up when it felt like it. What would cause it to be sporadic? It might be good to know for future reference.