Are you ordering from a country outside of the county of your account? I have a US Steam account and in te past few days, I've has to change the residency option to Korea and the Philippines because I kept getting that error. Evidently, Steam checks the country of your IP.
As a matter of fact, I'm deployed right now so thats probably what it is. Will it change to the a local store based on the country I'm in at the moment, even though my home is in the States? How will this affect my purchases?
I haven't purchased anything from Steam in a couple years, mainly because I've received a lot of my games for free from promotions. So I'm still pretty new at this.