When logging into NFine (except with the admin account, which bypasses permisions), clicking on Menu 1 opens Window 1, and clicking on Menu 2 opens Window 2. However, when switching back to Window 1 and performing an operation, no permissions are detected. Debugging reveals the issue in the HandlerAuthorizeAttribute class:

private bool CheckActionAuthorization(ActionExecutingContext context)
{
    var userProvider = OperatorProvider.Provider.GetCurrent();
    var roleId = userProvider.RoleId;
    var moduleId = WebHelper.GetCookie("nfine_active_module_id");
    var actionPath = HttpContext.Current.Request.ServerVariables["SCRIPT_NAME"].ToString();
    return new RoleAuthorizationService().ValidateAction(roleId, moduleId, actionPath);
}

The moduleId value is incorrect. Checking the frontend tabManager.js file:

addTab: function() {
    $("#header-nav>ul>li.open").removeClass("open");
    var moduleId = $(this).data('module-id');
    if (moduleId) {
        top.$.cookie('nfine_active_module_id', moduleId, { path: "/" });
    }
    var url = $(this).attr('href');
    var menuTitle = $.trim($(this).text());
    var tabExists = false;

The cookie is set here when creating a new tab, but the tab activation event doesn't update it:

activateTab: function() {
    var tabId = $(this).data('id');
    if (!$(this).hasClass('active')) {
        $('.mainContent .app-iframe').each(function() {
            if ($(this).data('id') === tabId) {
                $(this).show().siblings('.app-iframe').hide();
                return false;
            }
        });
        $(this).addClass('active').siblings('.menu-tab').removeClass('active');
        $.tabUtils.scrollToTab(this);
    }
}

The solution is to add a data-module-id attribute when creating the tab and update the cookei when the tab is activated:

addTab: function() {
    $("#header-nav>ul>li.open").removeClass("open");
    var moduleId = $(this).data('module-id');
    if (moduleId) {
        top.$.cookie('nfine_active_module_id', moduleId, { path: "/" });
    }
    var url = $(this).attr('href');
    var menuTitle = $.trim($(this).text());
    var tabExists = false;

    $('.menu-tab').each(function() {
        if ($(this).data('id') === url) {
            if (!$(this).hasClass('active')) {
                $(this).addClass('active').siblings('.menu-tab').removeClass('active');
                $.tabUtils.scrollToTab(this);
                $('.mainContent .app-iframe').each(function() {
                    if ($(this).data('id') === url) {
                        $(this).show().siblings('.app-iframe').hide();
                        return false;
                    }
                });
            }
            tabExists = true;
            return false;
        }
    });

    if (!tabExists) {
        var tabHtml = '<a href="javascript:;" class="active menu-tab" data-id="' + url + '" data-module-id="' + moduleId + '">' + menuTitle + ' <i class="fa fa-times"></i></a>';
        $('.menu-tab').removeClass('active');
        var iframeHtml = '<iframe class="app-iframe" id="iframe' + moduleId + '" name="iframe' + moduleId + '" width="100%" height="100%" src="' + url + '" frameborder="0" data-id="' + url + '" seamless></iframe>';
        $('.mainContent').find('iframe.app-iframe').hide();
        $('.mainContent').append(iframeHtml);
        $.loading(true);
        $('.mainContent iframe:visible').load(function() {
            $.loading(false);
        });
        $('.menu-tabs .page-tabs-content').append(tabHtml);
        $.tabUtils.scrollToTab($('.menu-tab.active'));
    }
    return false;
}

Then update the activateTab function to set the cookie:

activateTab: function() {
    var tabId = $(this).data('id');
    if (!$(this).hasClass('active')) {
        top.$.cookie('nfine_active_module_id', $(this).data('module-id'), { path: "/" });
        $('.mainContent .app-iframe').each(function() {
            if ($(this).data('id') === tabId) {
                $(this).show().siblings('.app-iframe').hide();
                return false;
            }
        });
        $(this).addClass('active').siblings('.menu-tab').removeClass('active');
        $.tabUtils.scrollToTab(this);
    }
}

This framework is very helpful for beginners, especially because fixing bugs improves your understanding of its inner workings.