function pageLoad(sender, args) {
    var pageRequestManager = Sys.WebForms.PageRequestManager.getInstance();
    if (pageRequestManager) {
        var isAsyncPostback = pageRequestManager.get_isInAsyncPostBack();
        if (isAsyncPostback) {
            tb_init('a.thickbox, area.thickbox, input.thickbox');
        } 
    }
}