URGENT - Can't checkout

Question

AFAIK there is nothing that has been changed over the last week but for some reason checkout is not possible, I've whittled it down to a problem in op_checkout.js::Review::nextStep:

nextStep: function(transport){
    console.log('opcheckout.js => Review::nextStep');
    //console.log(transport);
    //console.log(transport.responseText);
    if (transport) {
        console.log(transport); // THE PROBLEM
        try{
            response = eval('(' + transport.responseText + ')'); //FAILS 
        }
        catch (e) {
            response = {}; // GOES HERE
        }
        if (response.redirect) {
            this.isSuccess = true;
            location.href = response.redirect;
            return;
        }
        if (response.success) {
            this.isSuccess = true;
            window.location=this.successUrl;
        }
        else{
            var msg = response.error_messages;
            if (typeof(msg)=='object') {
                msg = msg.join("\n");
            }
            if (msg) {
                alert(msg);
            }
        }

        if (response.update_section) {
            $('checkout-'+response.update_section.name+'-load').update(response.update_section.html);
        }

        if (response.goto_section) {
            checkout.gotoSection(response.goto_section, true);
        }
    }
},

Answer 1

Fixed by doing the following;

In app/design/frontend/default/your_theme/template/checkout/onepage/review/info.phtml Replace the line number 81 in info.phtml

with

review = new Review('<?php echo $this->getUrl('checkout/onepage/saveOrder', array('form_key' => Mage::getSingleton('core/session')->getFormKey())) ?>', '<?php echo $this->getUrl('checkout/onepage/success') ?>', $('checkout-agreements'));