Emirates Bookings using Qantas points departing from HK (an error has occurred in our central database)

Been trying to book the classic rewards flight from Hong Kong to Dubai and Dubai to Rome on the next day flying Emirates. I had no problem booking the flights individually.

However, if I try to book these two flights together via "Multi City", I'm able to select all the flights and passengers, but it popped an error before the payment says : "An error has occurred in our central database. Please contact us for further information"

I called Qantas HK office, the customer said they couldn't locate any tickets in their HK ticketing office, but they could locate the same tickets in Australia ticketing office. The tax, however, would be charged in AUD which is at least 5 times than what was shown on the website booking.

Anyone has experienced this before?