For everyone that is getting errors when trying to link your Qantas number with your Membership Rewards account, I was getting this error online and via the phone. I have one of the old 7 digit account numbers, but apparently the new ones are 10 digits. I went ahead and added three zeros in front of my account number and voila it linked. Will see if it holds, but I think this will solve the issue.

If anyone has better info, please update.