We have a bug in the template that is used to create users in Professional & Enterprise.
The list of Orgs a user can have permissions on is inadvertanly being hidden, and hence when the data is submittined it is rejected as this is a required attribute.
A work-around is to use Open-AudIT Community to create users.
Ths bug will be fixed in the next release.
Apologies for any inconveinence caused.