If you are getting a "Sorry, no quotes are available for this order at this time." or a "This shipping method is not available" message under the "Shipping methods" section in the checkout, it is because your shipping methods don't have enough information about the customer/order to display any rates. In 99% of the cases, this is because you are using a shipping method that uses for example the customers postcode in order to calculate the shipping costs. Until the customer has entered a zipcode, there is no way for the shipping method to display any prices.
A few examples of shipping methods that require a zipcode: * FedEx * UPS * Bring (Norwegian)
The reason you can choose field is that you often need to display individual prices/taxes based on the customer's location. For example many stores offer different shipping methods to different countries. By enabling this feature for the "Country" field, OneStepCheckout will automatically update the available shipping methods along with prices when the customer changes their country. This also affects taxes - if you need to display tax to California only, you can choose "State" as a field and it will update once it changes.
To fix the issue with "No quotes are available", just enable the feature and choose the "Postcode" field and reload the frontend. It should now update once you enter a valid zipcode.