The network that Hyperborea is on may be affected due to a switch of routers that connect it to the Internet. Hyperborea may be unreachable during the maintenance window. Maintenance is scheduled for 21 february 2006, between 4am and 6am GMT. Check timeanddate.com to convert that to your local time, if required.
For full details, see Imgar's post on the adventurer's guild board.