Having same problem
Everything works except that after the order it doesn't take you to the success page.
The order is good as I see it in Authorize.net
I can browse to the success page and it shows everything perfectly.
I made the change ?empty=true; but that really doesn't affect anything unless the cart is empty.
Should I be putting in success.php in the redirectURL? It seems that this would realy "jack" things up because it would then not get to the email routine.
For me, after the order (press submit order) it comes right back to submit order, but the order is good. I seee in Authorize.net, I get the email confirmation and I also output the value of $WA_Store_Cart->redirStr which is the success.php page.
I'm sure it is soo simple I'm missing it right in front of my face.
Here's a link to try in out: soleus-running-262-watch2.php?ProductID=29
I set the product at .25 and shipping at .25. Also, I'll delete the charge in Auth.net if you are inclinded to test it out.
PS. Thank you for the help.