Normally, HTTP 404 is a 'Page Not Found' error.
If you go into IIS Manager and look at the site you installed Web Management Console onto, if different from the site you installed Web Client onto, do you see the 'WebManagementConsole' virtual directory?
If so, are you using the url that you used for Web Client, which is similar only instead of using something like servername.domainname.com/GP, you'd use servername.domainname.com/webmanagementconsole instead?
Thanks