Default User Type = Administrator?!

Hi everyone,

I've got a testing environment with an MS-SQL datasource with integrated security configured for RDM.
When a new user connects to the DB an error message is displayed, that the user cannot be found.
After a restart of RDM, everything works fine and the user is created. However, it is then created as an Administrator, which I'd like to prevent from happening.
New users should always be normal users. Unfortunately I cannot find the setting for this.

Is anyone able to help me out? :)

Cheers,
Mark