Ajax call does not work for this simple code

by

You have a space in your function name on the action call,

   add_action( 'wp_ajax_nopriv_ MyAjaxFunction', 'MyAjaxFunction' );  
   add_action( 'wp_ajax_ MyAjaxFunction', 'MyAjaxFunction' );

…should be,

   add_action( 'wp_ajax_nopriv_MyAjaxFunction', 'MyAjaxFunction' );  
   add_action( 'wp_ajax_MyAjaxFunction', 'MyAjaxFunction' );