everytime I go to http://msm.live.com/app/default.aspx, a certificate error occurs.
Does anyone know if there is another way to register an application in order to use Windows Live SDK?
The certificate error can be ignored – the certificate expired yesterday (June 9th) but is otherwise valid.
The second, "Server Error" is misconfiguration at Microsoft's end, and there is nothing you can do here. You'll have to wait for Microsoft to fix it.
There does seem to be another way to register an application: Go to https://live.azure.com/, sign in with your Live ID, and you will get redirected to an "Add Application" page (at https://manage.dev.live.com/AddApplication.aspx).