Magento 1.9 – How to Change Checkout/Onepage Layout Based on Condition

The cleanest way to do this is will use observers and custom layout XML. For that you will need to create your own extension. Inchoo has a nice hello world article that should get you started and you can read more about observers in this Magento Board post.

You will need to hook the controller_action_layout_load_before event. Add this to your config.xml.

<controller_action_layout_load_before>
    <observers>
        <[module]>
            <type>singleton</type>
            <class>[module]/observer</class>
            <method>addLayoutHandleObserver</method>
        </[module]>
    </observers>
</controller_action_layout_load_before>

Your Observer would use your code to check for the specific product and if present add a layout handle to the generate Layout XML. This will enable us to target it from a layout xml file.

class [Namespace]_[Module]_Model_Observer
{
    public function addLayoutHandleObserver(Varien_Event_Observer $observer)
    {

        $items = Mage::getSingleton('checkout/session')->getQuote()->getAllItems();

        $logo_cart = false;
        foreach ($items as $_item) 
        {
            $get_attributes = $_item->getProduct()->getTypeInstance(true)->getOrderOptions($_item->getProduct());
            $attributes = $get_attributes['attributes_info'];
            foreach($attributes as $attribute) {
                if($attribute['value'] == 'Has Logo') {
                    $logo_cart = true;
                    break;
                }
            }
           if ($logo_cart) break;
        }

        if ($logo_cart)
        {
            $layout = $observer->getAction()->getLayout();
            $layout->getUpdate()->addHandle('checkout_has_logo');
            $layout->generateXml();
        }

        return $this;
    }
}

Now we can add some custom layout updates from, for example, the local.xml.

<checkout_has_logo>
    <reference name="checkout.onepage">
        <action method="setTemplate"><template>checkout/onepage_logo.phtml</template></action>
    </reference>
</checkout_has_logo>

i think this error does have its origin in some eav attribute validation in the saveBillingAction like here: https://github.com/bragento/magento-core/blob/1264aee821b451b3c88e55659cd1ee79d3b324af/app/code/core/Mage/Checkout/Model/Type/Onepage.php#L284

I'm not 100% sure if this error comes from this, but you could check the eav_attribute table.

The customer should have the eav_entity_type id 1 (at least for me) and the custoemr address should have 2. (you can also look them up in the eav_entity_type table).

In the eav attribute table, theres a column 'is_required'. Although, its weird, that the attribute is empty in the message, you might find an attribute here, that is required (and then validated) in the table but not filled in in your checkout process.

It might also be a cache issue. If I'm recognizing corretly, there is a nasty cache for the eav attributes that could actually be responsible for such behaviour (given you changed or maybe deleted a customer or address attribute recently)