Yeah me too. I tried a number of times to do it online. Called VIP and the agent was stumped too. I'd waited for ticketing etc and everything was fine. HBA agent had to do some backend magic to force it through.
With that particular recent case I had, it was on an Amex issued ticket (can you say "travel credit"? 
), though agent agreed that should not have been a factor. It was just weirdly glitchy.
