When you request the page ContentManager.aspx in the admin folder, it's just show blank page .

Since there is no module id passed as parameter via URL we have to redirect the request to catalog page ContentCatalog.aspx and that done by one of the following :

1: in the BindControls method replace :

if (moduleID == -1)
{
//log.Error("moduleId was -1 in BindControls");
return;
}

with :

if (moduleID == -1)
{
//log.Error("moduleId was -1 in BindControls");
WebUtils.SetupRedirect(this, SiteRoot + "/Admin/ContentCatalog.aspx");
return;
}

2: for better performance and avoid unnecessary code calls but that code in Page_Load after LoadSettings();