Conflict between All in One Webmaster and Event Organiser

Thanks Steven,
AIO Webmaster does indeed also use menu position 5.
after reading your codex entry I added the following code to my themes functions.php

add_filter( 'eventorganiser_menu_position', 'my_callback_function', 10, 1 );
function my_callback_function( $menu_position ){
	//$menu_position = 7; // Positions Events menu item below AIO Webmaster menu item.
	$menu_position = 20; // Positions Events menu item below Pages menu item.
	return $menu_position;
};