Positions assigned to Roles

Hello! 

I am currenty using the trial version of Aris Architect (version 97.1.0.98111197) while working on a uni project, and I am trying to assign positions on the org. chart to roles but to no avail, Aris won't let me! Do you have any idea why this is happening? I had the impression that is exactly the point of roles and positions, eg. that a roles can be comprised of one or many positions.

Thank you very much in advance for your help!