That thin-set is garbage. Do not use it at all.
We try and not use any thin-set older than 3-6 months.
I to recently bought an expired bag of Laticrete thin-set. It's in the truck ready to return to the place I bought it from.
Laticrete makes the best packaging in the business but two year old thin-set will be nothing more than sand once mixed.
Send it back.
If you get any grief over it call up LAticrete Customer Service and they will set the seller straight.
Often product gets poorly shuffled in a warehouse and this could be the result of this. Or a savy warehouse manager was trying to pass off dated product on you.
Either way your out the trouble to go back and switch it.
ALWAY CHECK THE DATE CODES BEFORE LEAVING A STORE!!!!
This is one of my own rules and I broke it just three weeks ago. And read the bags - often there are primers or other liquids these products detail for slurry coats or unique installs.
You can find the local Laticrete offices here and look up their phone number. http://www.laticrete.com/contact_us.aspx