Do not show scroll button in second visit in Simple modal + slim scroll

Question

I am using Simple modal "jquery.simplemodal.1.4.4.min.js" and slim scroll "jquery.slimscroll.min.js" to popup and make a div scroll. Everything is fine working when I get first popup but when I close that popup using $.modal.close() and again I open it then overflow scroll button is not showing and only the scroll bar is there. What could be the problem ? Thanks in advance.

Update

Slim Scroll code:

$('#add_group_member_div').slimScroll({
 position: 'right',
 height: '130px',
 size: '10px',
 railVisible: true,
 alwaysVisible: true
});

Simple modal css code:

#simplemodal-container {
    width:709px; height: 464px;
    border: 4px solid #D0D2D3;
    background: #FFFFFF;
    -pie-background: #FFFFFF;
    border-radius:25px;
    display: none;
    position:relative;
    behavior: url("../css/groupmgmt/PIEFiles/PIE.htc");
}

Answer 1

I had faced & solved the issue by using pageLoad().

try this,

 function pageLoad() {
               $(function () {
                         $('#<%=ReportingEmployeesListPanel.ClientID %>').slimScroll({
                             position: 'right',
                             height: '500px',
                             width: '450px'
                         });
                     });
                 }