Originally Posted by
SQ421
JNB-xLHR-DXB-xLHR-DFW-xPHX-xANC-xPHX-ORD-MIA-xDFW-SYD-AKL-PER-CBR-SYD-JNB
Best I can think of is the AKL-PER service which is seasonal (though I've obviously selected the flight on a date it is operating) that is causing troubles.
YGM
I was able to set up your itinerary using the online tool; it priced up OK and seemed perfectly OK
So I don't understand why you are having the difficulties you are having
Perhaps try clearing your cookies and stuff like that, or maybe use a different browser (I find the tool seems to work better using Chrome rather than InternetExplorer)