Help with STP error messages please

Can somebody please steer me in the direction of a list of STP error messages and, most importantly, what they mean.   I've just had the following response which has left me completely nonplussed - and the weblink in the message is not active.

The element 'AddressDetailsPostal' in namespace 'http://sbr.gov.au/ato/payevnt' has invalid child element 'CountryC' in namespace 'http://sbr.gov.au/ato/payevnt'.  List of possible elements expected: 'Line1T' in namespace 'http://sbr.gov.au/ato/payevnt'.  Hint: while processing parent element [AddressDetailsPostal] child mandatory element [Line1T] was expected but not found