Remote Authenication

My organization just turned on the remote authentication option in order to use a single sign on from active directory. It works with everyone that was created and invited as a portal user prior, but new users can not sign in. It displays a message saying the user does not exist or is deactivated. When we try to add them as a contact and invite to the portal as we did before, the option to invite no longer shows up. Is this a bug or am I missing something?