Attempt to work around IE Ajax issue by hardcoding Ajax URL.

gce-hardcode-ajax-url.php

<?php
/*
Plugin name: Hardcode AJAX URL for Google Calendar Events
*/

function gce_hardcode_ajax_url() {
  if ( defined( 'GCE_GENERAL_OPTIONS_NAME' ) ) {
		$options = get_option( GCE_GENERAL_OPTIONS_NAME );

		wp_localize_script( 'gce_scripts', 'GoogleCalendarEvents', array(
			'ajaxurl' => 'http://www.ledøjeforsamlingshus.dk/wp-admin/admin-ajax.php',
			'loading' => $options['loading']
		) );
	}
}

add_action( 'wp_enqueue_scripts', 'gce_hardcode_ajax_url', 99 );