This one comes from a numerological study of the Bible, and using 'hidden' messages to extrapolate Judgement day.
This has been done several times, and most recently, if I remember right, in '98, when it didn't happen they said they made a error in computation. And went back to it.
The sad thing is that a lot of these folks have sold off their homes, quit jobs and such because "Hey, who needs that shit when the world ends in a week?" There was a local news story about how a family blew their savings, their kids college funds, and are waiting to be 'taken up' now. I have no issues with these folks ruining their own lives with this stuff, but putting your kids in a horrid position for their futures annoys.
Mark me, the day after it doesn't happen they will find a math error, or a missing hidden code that says its going to end in 2018 or such. And they will reboot and start again.
Myriads