Or so I think.
I have not been able to use this plugin for some time but thought I could just wait and see. Now I want it so checked some more why admin screen freak out when this is activated AND plugin gets auto disabled.
Check line 274 in wp-jump-menu.php - if wp-config.php is moved outside default folder it is not found and hell breaks loose.
A frantic Google search linked me to SVN of WP 2.9 wp-load file so what could go wrong? But http://core.svn.wordpress.org/branches/2.9/wp-load.php and I now use
require_once( dirname(ABSPATH) . '/wp-config.php' );
require_once( ABSPATH . 'wp-config.php' );
and plugin suddenly works :)