Error after hitting "finish"

-- url of the page with the problem -- : www.ronan.com/products/shop-our-products
-- HikaShop version -- : Essential to Business
-- Joomla version -- : 1.5.22
-- PHP version -- : unsure
-- Browser(s) name and version -- : Mozilla - most recent
-- Error-message(debug-mod must be tuned on) -- : Error_message

Hello,
I tried doing a test checkout with my credit card. I created a 50 cent item so that I could do this and then selected free shipping at check out. I entered my correct credit card information, and then when I select "Finish," I get "An error occurred" at the top of my page. Since it's so vague, not sure where to troubleshoot. Please help See attache screenshot.

Thank you.