Trouble Updating Virtuemart

[ZoBabe]

Joomla 2.5.27
Virtuemart 2.6.8
PHP 5.4.30

After upgrading to 2.6.10 on one site 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.

  I think this is related to a problem with the search box after attempting to upgrade. The search box remains stuck on one category, and won't search the whole shop, or any other category. This is the the same category that the checkout button redirects to after upgrade.

  I'm wasting way too much time trying to figure out what's going on here, and think I need some one on one support to help debug.
  Anyone interested?
  Z