The selected configuration for displays could not be applied

Solution 1:

**First need to install the restricted drivers for access to aticonfig

I had the same problem. Run sudo aticonfig --initial, to re-initialize your configuration files.

Now I'm not sure if restart was necessary here or not.

Now run 'sudo amdcccle' and you'll be able to configure dual display. Go to Display Manager and choose Multi-display desktop with display(s)... in Multi-Display tab for both monitors. **restart after this, Then disable the "mirror monitors" option in the Ubuntu display settings.