You said you have UPS, USPS and Flat Rate shipping modules ... but now you are saying that you are using Zone Rate ...

What all shipping module(s) do you actually have installed?

1 Only have installed shipping module you are using, if not using them click on them and click REMOVE ... do not leave them set to disabled ...

2 If using Sort Orders on 1 or more shipping modules make sure that you use a Sort Order on ALL shipping modules and ALL shipping module Sort Orders must be unique ...