I am setting up a 3910 and it will only allow one admin login, if another admin user logs in, it throws the current user out to the login screen.

Is there a way to have two admins connected at the same time? We don't have this problem with our 3900's

Draytek have always done that, its not unique to the 3910 - look under System Maintenance >> Administrator Password Setup and see if anything on there helps (local user?).
I would test myself but it will probably need a reboot and im working at the moment.

We haven't had that with the 3900's that we use.

3900 is Linux OS, 3910 is DrayOS, what I should have said all the DrayOS drayteks ive had, have always done that.

Possibly a non-admin user can also log on at the same time... not sure though.