fix bug in zencart 1.5 - one country in checkout causing error

We have updated zen cart from 1.3 to 1.5 a couple of months ago and only now discovered that when checking out, if New Zealand is selected, it produces an error, plus the zone rate shipping module no longer correctly recognised New Zealand address. I guess its a simple fix of country code in the database or something like that. Please specify if you are online and able to start immediately.