I have added Transmission PPA. After adding PPA, when I tried to open software updater I got the following messege.

Failed to load the package list

This is a serious problem. Try again later. If this problem appears again, please report an error to the developers.

Even I could'nt open software sources, ubuntu software center, and sypnatic package manager.

What I have to do. Is there any command to remove the PPA.