Did you changed the date of your computer, even 
temproraily ? In that case, your browser may 
consider that the cookie is expired and delete 
it...

The site was not reachable for a few hours 
yesterday and today : The telecom disconnected 
several lines by mistake in one of their central.
One of those line is used to connect two parts of 
our network.

Cheers,
Yann Stettler