Critting the undead?

[TheBlueFox]

A friend and I have noticed something strange when going through deleras tomb. We've been critting the undead. It doesn't happen often, but we've checked our gear and our enhancements, nothing we have provides any fortification reduction.

I'm a lv10 paladin and he's a lv10 ranger, is there something we have that might make us crit? Its all kinds of undead too, archers, warriors, even the arcane. Its rare, but it happens. Mostly for him.

(Party: [Party] XXXXXXX: (Combat): You roll to confirm a critical on Delera Omaren. You roll a 16 (+27): Critical Hit!
(Party: [Party] XXXXXXX: (Combat): You hit Delera Omaren for 116 points of slash damage.