in case anyone is looking for a solution, try this.
First, ensure that you have the necessary permissions to
Execute SQL Query;
check config.php
ACP > Maintenance > Execute SQL Query
in the box (Manual QueryOnly one query can be run at a time. Once a query is executed it can not be reversed), enter the following;
Code:
select username from vb_post where postid = XXXX;
where XXXX is the Xth post
Results will return the member who made the Xth post