Can't login as root user from login window (not password error)

I just installed the system with the latest ISO (folder server MATE). When i reboot I can’t use the root user account. The login window does not give any explicit response after I entered my correct password for ROOT. I can only log in using my other user account.

The ROOT account password works fine in terminal.

The login window never says my root password is wrong, nor does it confirms its correct. It just does not seem to take notice and keeps staying the way it was. Unless i use my other account.

Can anyone give me some pointers to fix this? Thanks a lot.