Gnome-flashback is not operating properly

I am facing a new problem on my Dell M70 running 18.04. I was running the Gnome Session Flashback with no problems. But after adding a new user, I cannot open the System Settings. Not only that, it appears that freezes the system to the point that I cannot shutdown nor reboot the system. I can do it only with the power button. I tried re-installing gnome-flashback, gnome-flashback-common and gnome-session-flashback but it didn't help. On the other hand if I logon under the Ubuntu desktop environment I can open the system settings and do everything.

I would appreciate any help.