PayPal error "Call to a member function on a non-object

[brendanl79]

(Cross-posted from Mods forum)

Testing payment process with PayPal sandbox.

The PayPal payment completes OK, but when I click "Continue" at the last PayPal screen to return to my website, I get:

Fatal error: Call to a member function on a non-object in [redacted] ... /catalog/includes/modules/payment/paypal_ipn.php on line 521

The line in question reads:
$order_total_modules->apply_credit();

xargs grep from /catalog for " apply_credit" (with leading space):
./includes/classes/order_total.php: function apply_credit() {
./includes/modules/order_total/ot_coupon.php:function apply_credit() {
./includes/modules/order_total/ot_gv.php: function apply_credit() {

[stevew]

I am also have the same problem... Any help is a god send!