I have recently purchased a EC1279U-RP and can confirm all works fine.
had a few teething problems with services and performance, this maybe don to a lot of data over 15TB worth and the unit takes a while to read and catalog it all but after a few days it all appears to have settled down and work well.
what OS ore you using on the mac?
have you ensured the firmware is up to date (3.6.1 I think)?
can you log in as the admin user?
what about if you click on the go menu down to connect to server and type afp://(TYPE
YOUR IP ADDRESS)
are you cabled or wireless as I have experienced problems when connecting wirelessly with certain routers i.e. netgear in particular with old firmware, try using a wire.
also try creating a new user on your mac log into that user and see if that works?
all the best