Error When Creating New User in UME - GRC 5.3, but works via Backend

All,

When I try to create a new user in the User Management (UME), I get a very generic error message: "An error occurred; contact your system administrator". However, if I create the new user in the ABAP - backend first then he/she will show up in the UME and I can add Java roles to the user in the UME and he/she can work without issues. Therefore: do you always have to create GRC administrator users in the backend first or should it work when first creating in the UME as well?

Thanks, Joerg