All scripts seem to be present but AJAX submission not working

see https://s140452.gridserver.com/contact/ for reference

I'm running 1.6.3.1.2

I have the following scripts loading in the header:

<script type='text/javascript' src='https://s140452.gridserver.com/wp-includes/js/jquery/jquery.js?ver=1.7.1'></script>
<script type='text/javascript' src='https://s140452.gridserver.com/wp-content/plugins/gravityforms/js/jquery.json-1.3.js?ver=1.6.3.1.2'></script>
<script type='text/javascript' src='https://s140452.gridserver.com/wp-content/plugins/gravityforms/js/gravityforms.js?ver=1.6.3.1.2'></script>

plus

<iframe style='display:none;width:0px; height:0px;' src='about:blank' name='gform_ajax_frame_1' id='gform_ajax_frame_1'></iframe>
                <script type='text/javascript'>function gformInitSpinner_1(){jQuery('#gform_1').submit({eventName : 'ajaxSpinner'}, function(){jQuery('#gform_submit_button_1').attr('disabled', true).after('<' + 'img id="gform_ajax_spinner_1"  class="gform_ajax_spinner" src="https://s140452.gridserver.com/wp-content/plugins/gravityforms/images/spinner.gif" alt="" />');jQuery('#gform_wrapper_1 .gform_previous_button').attr('disabled', true); jQuery('#gform_wrapper_1 .gform_next_button').attr('disabled', true).after('<' + 'img id="gform_ajax_spinner_1"  class="gform_ajax_spinner" src="https://s140452.gridserver.com/wp-content/plugins/gravityforms/images/spinner.gif" alt="" />');});}jQuery(document).ready(function($){gformInitSpinner_1();jQuery('#gform_ajax_frame_1').load( function(){var contents = jQuery(this).contents().find('*').html();var is_postback = contents.indexOf('GF_AJAX_POSTBACK') >= 0;if(!is_postback){return;}var form_content = jQuery(this).contents().find('#gform_wrapper_1');var is_redirect = contents.indexOf('gformRedirect(){') >= 0;jQuery('#gform_submit_button_1').removeAttr('disabled');if(form_content.length > 0){jQuery('#gform_wrapper_1').html(form_content.html());jQuery(document).scrollTop(jQuery('#gform_wrapper_1').offset().top);if(window['gformInitDatepicker']) {gformInitDatepicker();}if(window['gformInitPriceFields']) {gformInitPriceFields();}var current_page = jQuery('#gform_source_page_number_1').val();gformInitSpinner_1();jQuery(document).trigger('gform_page_loaded', [1, current_page]);}else if(!is_redirect){var confirmation_content = jQuery(this).contents().find('#gforms_confirmation_message').html();if(!confirmation_content){confirmation_content = contents;}setTimeout(function(){jQuery('#gform_wrapper_1').replaceWith('<' + 'div id=\'gforms_confirmation_message\' class=\'gform_confirmation_message_1\'' + '>' + confirmation_content + '<' + '/div' + '>');jQuery(document).scrollTop(jQuery('#gforms_confirmation_message').offset().top);jQuery(document).trigger('gform_confirmation_loaded', [1]);}, 50);}else{jQuery('#gform_1').append(contents);if(window['gformRedirect']) gformRedirect();}jQuery(document).trigger('gform_post_render', [1, current_page]);});});</script><script type='text/javascript'> jQuery(document).ready(function(){jQuery(document).trigger('gform_post_render', [1, 1])}); </script>

But the AJAX submission and error handling is not working. I have <?php wp_head(); ?> in the header and <?php wp_footer(); ?> in the footer. What's going wrong here?

Thanks for your help!