I am having a serious problem.

My website is www.reasonably-priced-caviar.com
I am running Joomla 1.15.19, VirtueMart 1.1.4 and Artio JoomSEF 3.7.4 with the VirtueMart extension version 2.0.33.

When I try to order a product. on Step 2 of the process I click the checkout button and it redirects me to my site index page. I have checked through the FAQ's on this site and the forums and found no solution that works.

IN my JoomSEF control panel the Set Server QUERY_STRING is set to "Yes"
I've tried the "Fix index.php links" setting with both No and Yes...and the same thing happens every time.

Nothing is working and I need a solution to this problem ASAP! HELP!!!!