As we have seen so far the app does not require the Mobile feature enabled @ this point. What seems to be add with this particular installation is that the error seems to be happening based on users, as you have described that it does work for some users and not for others.
What happens when u create a new user ? Does the app work with the new user ? Reason I ask is because unless there are differences at the user lever admin side, then all that is left is password entry.
With Verion 1.1 the authentication requires the following ( and I know you have this correct )
1) Full email
2) Password)
3) Domain name inclusive of http or https exp
https://webmail.aderium.com
(no extra / after the domain name, we are addessing this in ver 1.2)