Authorize.net/OScommerce/Credit an Order issue

I bought an OSCommcerce web template a few weeks back and have got it all set up and running and was using paypal for payment, I got tired of that and went with [login to view URL] to do credit cards, the account is set up and working but after I entered in my info in the authorizenet payment module that came with the template I started to see problems. After they enter in their card info and hit comfirm it goes back to the customer log in page instead of going to the checkout_process or successful order page.....credit card does get charged but no info on what product they ordered shows up and nothing goes to the orders page in my OSC admin. I want someone to work out all the bugs and help me get my payments going smoothly. Thanks.