Not, as previously thought, because her and husband Ben Affleck were 'working'. No: lice.
Basically, the actress had to deal with her kids coming home with headlice - and ended up getting them herself because not even celebrities are immune to small animals living in your hair. Not even actors starring in popular crime movie Gone Girl (Ben Affleck is in Gone Girl and it's very good). The whole family had to put foul smelling nit lotion in their hair.
But back to the Clooney wedding. During this whole nitty period, Jen ran into George Clooney at a party, and didn't make a great first impression: 'We show up and the first person I see is George Clooney, and I'd never met George Clooney. I was kind of like, "Ah, he's so handsome! Like, oh, my God!"' she revealed on The Tonight Show. 'So, I see him and I walk up to him and I'm chatting with him, just trying to act like it's cool...and I can see that he smells me, you know? But he's trying to be polite.'
'So, anyway, people keep asking why we weren't at George's wedding and we were both 'working' but I think he didn't want Licey there," Jen joked. 'He's like, "No, we don't need the Afflecks. We're OK!"'
Nowhere in this story does Jen confirm that George identified the weird smell as nit lotion - so maybe he just thought she smelt way too chemical-ly to be let loose on A-list wedding guests.
Either way, we reckon she's probably joking. There's no way Clooney wouldn't want the Affleck's at his wedding - what's a nit or two between friends?