Hello,
Best place would have been opening this correctly under CA Directory space as oppose to Identity Manger.
Anyway, before we get into more details on this, I would also like to inform you that we already announced EOS for CA Directory r12.0 SP14 and below starting Jan 31st, 2018 so my first suggestion would be not to use this release if you are getting started on CA Directory.
i.e.
CA Directory 12.0 SP14 and older End of Service Announcement
As for the problem now.. there is no management UI for the version you are using. What you have is DXmanager/DXwebserver to create, deploy and manage your CA Directory backbone. The UI, I believe you are referring to as the new management UI, is part of CA Directory r12.5 and r12.6 release. Please clarify.
As for JXplorer, it is an openSource product so it might help the cause if someone reported this problem on opensource community forums.
By the way, it is also important to know what platform you are using as the root case might also depend on that.
Thanks,
Hitesh