I tried installing tlp and Ubuntu tweak on my new Ubuntu(previously I had the same Ubuntu, but reinstalled it). When adding their sources, I got the error no ultimately trusted keys found.In the previous installation I did not get these errors.
Its something about PPA problems , I mean its all about Broken PPA's. all you need to fix them.If you want to know more why it has happen : http://trog.qgl.org/
To fix the issue , open your terminal and type as
Then launch the application with sudo
that will take care of your issue.