Advanced searching is still possible through this page:
But as john says, this is really a vBulletin issue.
To be honest, I very rarely use the Search functions of vBulletin, instead, I use an advanced google search and constrain it to the webassist.com/forums site by entering
in the google search box.
so to search for your string:
"The totals of the cart item amounts do not match order amounts"
I would enter the following in the google search box:
site:webassist.com/forums "The totals of the cart item amounts do not match order amounts"