After upgrading Magento from 1.5.0.1 to 1.5.1 a successful check out doesn't redirect to the confirmation page

After upgrading Magento to 1.5.1 when a customer orders their screen refreshed, but it doesn't redirect to the confirmation page and customers can push the place order button again and have their card charged again. Has anyone else stumbled onto this problem?

Thanks for looking

UPDATE:

After I checkout the server returns the following response:

Fatal error: Call to undefined method Mage_Payment_Helper_Data::getZeroSubTotalPaymentAutomaticInvoice() in /var/www/magentoba开发者_高级运维se/app/code/core/Mage/Checkout/controllers/OnepageController.php on line 503

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Turns out there was a patched file I made awhile ago that fixed a previous issue that was causing the conflict. The patched file was located in:

app/code/local/Mage/Payment/Helper/Data.php

I simply removed the file and everything is working fine.