Hello and welcome.
I just tried it on two different Macs - one running Snow Leopard and one running Yosemite. They both get the same error you are getting. It is something with their website, not your Mac.
I would try again tomorrow. I bet they are having server difficulties or it is currently offline for maintenance. I would guess it will be working again in the next day or two.
I know that the Flixster and UltraViolet sites were also having issues this weekend.
C