Problem upgrading to 2.6.10

[ZoBabe]

Joomla 2.5.27
Virtuemart 2.6.8
PHP 5.4.30

After upgrading to 2.6.10 on one site (http://www.pizzabagus.com) the checkout no longer works. When someone checks out, they are redirected to a category page, and no order is recorded. I have upgraded several other sites without any issue, so the problem is something specific to this one site. However, I have tried the default templates, and everything else I can think of, and the problem persists. So, for now, the only fix that works is rolling back to VirtueMart 2.6.8.

Have also posted this to the "commercial jobs" section, but thought I'd try here too in case someone has had a similar issue and can point me in the right direction.
  Any info would be greatly appreciated!