$(document).ready(function() 
    { 
        $('#ctl00_Body_lstMeses').change(function() 
        {
            $.blockUI(
            { 
                message: $('img#imgEspere'), 
                css: 
                { 
                    top:  ($(window).height() - 261) /2 + 'px', 
                    left: ($(window).width() - 261) /2 + 'px', 
                    width: '261px' 
                } 
            }); 
        
        }); 
        $('#ctl00_Body_lstRegimenes').change(function() 
        {
            $.blockUI(
            { 
                message: $('img#imgEspere'), 
                css: 
                { 
                    top:  ($(window).height() - 261) /2 + 'px', 
                    left: ($(window).width() - 261) /2 + 'px', 
                    width: '261px' 
                } 
            }); 
        
        }); 
    });