It's a dns error, in some locations periodically at the moment your isp tries to read a cahced version of the site which reads off the old ip the site used be on before we switched servers., I have spent countless amounts of time trying to get this sorted with the techs at the hosting company, but I just get fobbed off with something every time and nothing seems to get done about it.
I appologize that you can't get on and I it makes me more frustrated than you that this error keeps popping up.