Hi Cristiano:
Thanks a lot for this new answer, I had already implemented the logoff web service and is working fine, but we still have the problem because we don't want the users can sing on with the same user id in multiple devices, that is the reason we want to implement the Check for multiple logons option, but even this is killing the other sessions at the beginning, if the user that was working in the session that was killed were in the principal menu and hit any option there, the system is generating another session automatically, this is the actual problem, if they use the log off button, the session is killed and they are redirected to the log off page. please let me know if you have any other taught, I had send a ticket to SAP, but they did not answer yet, as soon as I get the resolution will share here.