I got the same error as you when I tried to install the script a couple of weeks ago. c:
I noticed that my host had switched my php version back to 5.2 for some reason and I didn't realize it. I changed my php version back and reinstalled the script under a subdirectory, and it worked then.
You could check if your php version is indeed version 5.3, and if it is, try reinstalling your site in a subfolder. c:
If you install it into a subfolder, you can easily have your users redirected from site.com to site.com/whatever by creating an index.php in public_html and adding this:
Code:
<?php
header('Location: http://www.yoursitehere.com/yoursubfoldername');
?>
If that doesn't work, try asking your host if mod_rewrite is enabled, and if it isn't, if they can enable it for you. c: