I have upgraded my ZenCart 1.5.6 site to 1.5.7c by doing a clean install of 1.5.7c, manually upgrading my custom template files using the 1.5.7c core files, and reinstalling the OnePageCheckout PlugIn. I had ceon-manual-card pay module installed in 1.5.6, but I am not reinstalling that since it is out dated and no longer supported. I also had SalesReport plugin in 1.5.6 but it is not installed in 1.5.7c yet. I have OnePageCheckout working, and am now trying to add PayPal Express Checkout.

I have PayPal connected as a sandbox. If I Log In to Zen Cart I can successfully check out with PayPal. I can also check out with PayPal as Guest, but only if I fill in the billing Name, address etc. on the checkout page. If I try to check out with "PayPal" button from the cart, bypassing the billing info page, I receive this error:
Code:
#1  trigger_error() called at [/includes/classes/OnePageCheckout.php:2323]
#2  OnePageCheckout->getTaxLocations() called at [/includes/classes/observers/class.checkout_one_observer.php:640]
#3  checkout_one_observer->update() called at [/includes/classes/class.base.php:118]
#4  base->notify() called at [/includes/functions/functions_taxes.php:286]
#5  zen_get_tax_locations() called at [/includes/modules/order_total/ot_tax.php:31]
#6  ot_tax->process() called at [/includes/classes/order_total.php:178]
#7  order_total->pre_confirmation_check() called at [/includes/modules/payment/paypalwpp.php:1542]
#8  paypalwpp->ec_step1() called at [/ipn_main_handler.php:75]
--> PHP Fatal error: Unknown/invalid billto address # for customer#. in /includes/classes/OnePageCheckout.php on line 2323.
I read that as the error occurring before the call to PayPal, but I thought using the "Checkout With PayPal" button from the cart, skipping the Billing Info page, should retrieve the billing/shipping data from PayPal. The test site exhibiting this behavior is at https://test.chessieshop.com
Any ideas?
Thanks,
Lars