When I try to store a new user as non superadmin I get the following warning:

ODOO WARNING - Access Error
Der gewünschte Vorgang kann aufgrund von Sicherheitsbeschränkungen nicht
 ausgeführt werden. Bitte kontaktieren Sie den Systemadministrator.
(Dokumenten Typ: Res Users Password History, Vorgang: create)     
The desired operation can not be performed due to security restrictions. Please contact the system administrator.
(Document Type: Res Users Password History, Routine: create)     

It seems not be an ACL issue because the user that should be able to create new users has either administrative settings or Access Rights permission.