Why does magento register at checkout not working sometimes? How to Auto login already registered customers?

Question

In my magento website, "Guest Checkout" is disabled. People need to register while they checkout. This works fine, as it is a default behaviour. But sometimes, people who register are not really registered, but considered as Guest.

This happens randomly. I don't have any idea what is going wrong. Can anyone help please?

note:

The website uses the default onepage checkout with minor modifications only in templates (jQuery additions for some attractive UI).

the output of running SELECT * FROM customer_group is:

running SELECT * FROM core_config_data WHERE path = 'customer/create_account/default_group' returned empty set.

Answer 1

At last found the problem, there was a custom modification, which didn't throw an exception, when already registered customer tries to register again. So, that customer was considered as a Guest [NOT LOGGED IN] customer.

The bad part is that, it was straight away done in core files, so I didn't find it until now.

I didn't want to mess up with these changes, so created an event-observer to automatically login, if the customer is already registered.

if(!Mage::helper('customer')->isLoggedIn()){
    $data = $evt->getEvent()->getControllerAction()->getRequest()->getPost('billing', array());
    $customer = Mage::getModel("customer/customer");    
    $email = $data['email']; //email entered in billing address section
    $customer->setWebsiteId(Mage::app()->getStore()->getWebsiteId())->loadByEmail($email);

    if($customer->getId()){
        Mage::getSingleton('customer/session')->loginById($customer->getId());
    }
}

Answer 2

You need to clear your cache and reindex the website. Flush all of the caches.