Just to follow up for anyone reading this thread. I received email this morning around 6:AM EDT from ShipSim.com Support saying they had fixed the issue and removed the debug code, and would I try again.
I did around 9:AM EDT, and I was able to order Ship Sim 2010 Extremes using my American CC without any issue. Unfortunately, as it's now release day, I've missed out on the extra content. But for those who had this particular issue yesterday, please note you should be able to order today.
Kudos to the ShipSim folks for a quick response and resolution to the ordering system.