Actually an error message doesn't appear if you change the Fastway script to check the 'city' details as well. What happens is that the customer just doesn't get Fastway as a shipping choice. The temporary workaround for me was this..

1.Make sure you have another shipping option chosen to use.(in my case it was a local pick-up)

2. Change the text in the includes/languages/english/checkout_shipping.php to say something like the following (about line22)...."TEXT_ENTER_SHIPPING_INFORMATION', 'This is either <br>1.Your prefered shipping method by choice,or<br>2.Your City name was typed incorrectly in your Shipping Details.<br>Please email us if youre unsure about the best way to spell your City to complete Checkout.');