Moodle networking (MNet)

I've followed the documentation, but i've got a problem, when using your server http://www.efaktor.no/nettverk1 (it works with another Moodle test instance on my server).

When i try (as an admin) to enroll my students to the courses on your server (clicking on Admin > Network > Enrollment and your server name), i've got this error message :
RPC enrol/mnet/available_courses:ERROR 2:Payload not signed: faultCode 7017 faultString IP-adressen din samsvarer ikke med den adressen vi har i oppføringen.

Don't understand why...