Plugin broken for 3.9.2

When activating the plugin I get the following error message:-

“The plugin generated 1864 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.”

Plus there are no links created for Appearance > Login Screen.

Can you please advise?

Cheers

Edit: re-installed again just incase something happened. But still the same result.
https://wordpress.org/plugins/mayo-login-screen/