Does this mean you upgraded a Live site without testing?
Tested. Everything else looked fine. Let's you go through the entire order process no problem.
What payment method was used?
PayPal
If PayPal ... go to Modules ... Payments ... write down all settings ... remove and >reinstall and reconfigure ...
I think I've done this about 5 times now.
Test site ...
Tested tested tested. Lot's O Bugs in here.
WARNING: always backup the database and site before attempting any changes, >upgrades etc.
Doesn't matter when your dealing with NEW orders.
WARNING: never upgrade a site without doing a test upgrade on a test site on a >test database and test all functions from create account, to ordering, to checkout, >to My Account, to Orders, to etc. etc. etc.
There are an awful lot of things to test here.