I'm guessing that the user account that you are logging in with has spaces in the postcode/zipcode in the delivery address. You can either remove the spaces in the database, or upgrade to Austpost v2.1.3
If there is no urgency to fix this you may want to wait another day or two and the latest 'ozpost' module will be made available (the current 'ozpost' module (that supercedes 'AustPost' has a couple of issues of its own).
Cheers
Rod




