This function comes from version 4.0.5,
and not from PHP 4 >= 4.0.0 as stated here.
So don't not waist time like I did searching for it.
http://www.php.net/ChangeLog-4.php
Version 4.0.5
30-Apr-2001
Added sybase_get_last_message() to the Sybase CT module. (Jan Fedak)