ok grazie, io ho risolto così:
Codice PHP:

$id 
$_POST['gb_delete_checkbox']; ;
                
$i=0;
                while(list(
$key,$value) = each($id))
                {
                
                    
$query "DELETE FROM gb WHERE id='$value' LIMIT 1";
                    
                    if(
mysql_query($query$db_conn)) $i=$i+1;
                    else die (
"Errore nella selezione del db");
                
                }