Is your ibay set to run php scripts.?
Do you have other php code running from the ibay?
Make sure your script is either php version 4.3.9 compatible or install the php 5 addon,
http://wiki.contribs.org/PHP5 Are you testing small files first, there are file size upload limits set in the php.ini file.
See php configuration by creating a file with a php extension such as phpinfo.php and place the below text in it
<?php
phpinfo();
?>
try simple measures first, as experienced as i am, i still have to do it.