If an update of the Magento Market Ready Germany or PAYONE extension broke your checkout, this may be interesting for you:
Yesterday I updated the Market Ready Germany extension to the new version 2.1.40 for one of my clients. The extension now has a dependency to the new PAYONE extension 3.0. After the upgrade of the extensions, the checkout was broken! If a payment method has been selected, one could not proceed with the review step. So what the heck happened?
The client does not use PAYONE. Since the PAYONE extension made some major problems in the past, I had disabled the extension with the key „Mage_Payone“. With the upgrade to the 3.0 version of the PAYONE extension, the extension does not have the „Mage_Payone“ key any more – the namespaces are now „Payone_Core“ and „Payone_Migrator“. After I disabled these two extensions, the checkout worked again without any problem. Dear extension developers: If the PAYONE extension is not set up, it should not have ANY effects on my installation. Under no circumstances it may break my checkout.
Update 2012-09-13:
PAYONE was really quick and contacted me today. They will try to fix the issue as soon as possible. I will keep you up to date here.
Update 2012-09-27:
PAYONE did a good job and fixed the problem quite fast. The problem was an overwrite conflict with Dsdata NoState, which is installed quite often in German shops. The new version 3.0.10 of the PAYONE extension is now compatible with the Dsdata NoState extension. I tested it and the checkout went well again. Thanks to PAYONE and their Magento partner noovias! Here is an explaining text directly from PAYONE and noovias:
The reason for this behaviour is two extensions trying to apply an rewrite, in this case the PAYONE Payment Extension 3.0 and the „Dsdata_NoState“-Extension. Within the release 3.0 of the PAYONE Extension an rewrite of Mage_Sales_Model_Quote_Address was implemented to extend the validation of an address. The „NoState“-Extension is rewriting this class too, that is the reason for the problems during checkout. Due to the „NoState“-Extension being used quite often, PAYONE decided to add compatibility. We adjusted the address validation of the PAYONE Extension to use the address validation of „Dsdata_NoState“, when this extension is installed and active.
Thereby a manual deactivation is no longer necessary.