mysql_insert_id()

I'm inserting data into a table with an auto_increment field. The data is going in perefectly (with the A_I field incrementing as it should; I can see this is true in the DB) and there is no errors being returned. However, when I try to executed the mysql_insert_id() function (immediately after the query), it is returning '0' (zero). Why? Here is my field definition: | ticket_number | int(15) unsigned | | PRI | 0 | auto_increment | I cannot see in the docs why it would fail and unfortunately, mysql_insert_id() does not return why it would have failed getting the auto_increment value. I'm using PHP 3.0.5 and any help anyone could offer would be greatly appreciated!! Chris