Authorize.net Transaction Declined When in Live Mode

Hey all

So, I've got Marketpress set up, a dedicated IP, SSL installed, https:// across the site, but when I moved from Test mode to Live, transactions are being rejected for some reason.

I'm receiving this error on the final payment page:

"There was a problem finalizing your purchase. This transaction has been declined Please go back and try again."

My site is at https://www.ledshineamerica.com and the product I was testing the transaction with is located at:
https://www.ledshineamerica.com/led-light-bulb-store/led-light-bulb-products/test-product

Any idea what might be causing this?
The API Login ID and Transaction Keys are exactly what are shown in the Authorize.net account information.

Thank you.