I don't use OpenAudit on IIS but you might use the [url=http://php.net/manual/en/function.phpinfo.php]phpinfo[/url] function to troubleshoot your config.
Create a test.php file in the root of your openaudit web directory with the following contents.
[code]
<?php
// Show all information, defaults to INFO_ALL
phpinfo();
?>
[/code]
Then browse to
http://<openauditserver>/test.php and review the output. It will tell you which INI file you're using and what modules you have enabled. Maybe this will help track down your problem.