I am having a similar problem and I followed all the steps in this thread. I activated the php.ini allow_url_fopen = On. I didn't do the .htaccess because it give me a 500 error and I read these only work in php 6 anyhow.
I am hosted on 1and1.com.
I also tested the :
<?php error_reporting(E_ALL); ini_set('display_errors','On'); echo file_get_contents( 'http://www.google.com/calendar/ical/161hkrdo0qrhfc6sj4s613gib4%40group.calendar.google.com/public/basic.ics' ); ?>
You can see the result here :
Which display the actual calendar. I looked into the error trough the firebug ajax-admin script and it cleanly give an error that there is no event.
I tried the calendar on a different site and it worked so it's defenitly my settings or my host :S.
The calendar I am working with is :
which is also copied locally to test here :
The php info shows that I have these on :
allow_url_fopen On On
allow_url_include On On
What else should I be looking for ?