The postage calculator in my listings is not working

[*kazumi*]

I have entered the size and weight correctly, selected the service but it does not show postage in the listing.  When you click the calculate link there is a message in red " Postage cost can't be calculated. Please enter a valid postcode."  But does not matter which postcode I enter the same thing happens.  What is wrong?  Other sellers' items in my search have the calculator working

Does anybody have any idea?