Off Site Log In Error

We have several laptops running ADSelfService Plus client. When they are off site they receive this error:

"Could not connect to the ADSelfService Plus server or Domain Controller configured in ADSelfService Plus is Down. Please contact your administrator"

These are domain computers that can successfully log in on site. We have had some success recommending users connect to their home wireless at the log in screen, but for several users, even when they connect to their home wireless at the log in screen, and confirm they are connected, they get this error when entering their user name and password.

These are computers on our domain and users logging in with domain accounts that have never had an issue with these machines logging in before ADSelfservice Plus.

Is there something we are missing?

Chris D