Problem with the creation of a new user

Hi!

II want to create new user in the database but i have this message: this entry already exists in the following tables (CUMI).

This user doesn't exists and we haven't deleted users.

When I am going to see in the table OUSR I have 19 users

But when I am going to see the table CUMI, it recognises an user code 20!

when I use the orange arrow near the user code 20, nothing happens.

SAP 2005 A PL 46

How can i do?

Thank you

Séverine