After I upgraded from 14.10 to 15.04 now whenever I log in, My wallpaper becomes distorted and a series of black and white hyphen-like bars appear vertically on the right edge of the screen.
This is talking about the same issue but does not provide any solution.
This is also a discussion to the related problem but I couldn't find my solution.
Is it a display driver issue or a configuration issue? how can I fix it?