Hi Blind1,
http://drc.edeliver.com.au/ratecalc.asp?Pickup_Postcode=3156
&Destination_Postcode=&Country=AU&Weight=280
&Service_Type=STANDARD&Height=25&Width=250&Length=290
&Quantity=1
As you can hopefully see, for some reason or other, there is no destination postcode being passed on to the server.
I've created an account in your store for further testing and have discovered that this particular problem goes away when logged in. However, the a couple of items I added to the cart didn't have any weight attributes, which produced a different error. When using the Austpost module all items MUST have the weights set.
SO, to see this module work as it should, you need to first log in and then add a few items to your cart (ensuring the items have weights).
This then leaves the question of WHY is it losing the destination post code when NOT logged in. Unfortunately I don't have an answer (yet)
I WILL suggest that you try DELETING
/includes/templates/CUSTOM/templates/tpl_modules_shipping_estimator.php
This will cause the zencart default module to be used. If this takes care of the errors we'll know that there is something amiss in this part of things.
If the exact same problem exists we'll have to start looking elsewhere.
Another thing you can try is to replace the original file
/includes/templates/template_default/templates/tpl_shipping_estimator.phpwith the one from the austpost zip file. PLEASE BACKUP THE ORIGINAL FILE FIRST. Restore it if it doesn't have the desired effect.
Cheers
Rod