Orders going through multiple times, or not at all.

[HopeD]

I am using Joomla 2.5.28, VM 2.6.17, PHP 5.5.31. I am using VirtuePlanet's SuperMart template.

When customers place an order, it either goes through multiple times or not at all. Customer information is not being saved on some orders. This doesn't seem to happen to registered users, only guests.
I tried multiple times using my own credit card and managed to get an order to go through, the page took over a minute to load though. It had some odd error messages, I've attached a photo of that as well as showing some blank "orders" and an order that came through several times.

The only thing I've recently changed settings-wise is the Mail Settings. Other than that, we've just been adding items.

I'd appreciate any help.