Thanks cardinalu so much, but, when I try to define it by add more line:
Ha ha, warning disapper, but I guess, is it OK?
And also in dashboard, some posts (not all) will appears this warning:
Notice: Undefined index: feat_slider in /Applications/MAMP/htdocs/wordpress/wp-content/plugins/wp-featured-content-slider/featured-content-slider.php on line 49
$custom = get_post_custom($post->ID);
$feat_slider = $custom["feat_slider"];
In this case, the global $feat_slider not working, ha ha ha. Sorry, i'm not good in PHP.
Many thanks in advance, and have a nice day, cardinalu.