after installing this plugin, WordPress displays this message:
'The plugin generated 6 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.'
and it's also affects the site layout.
However, at the end of mfplg.php file, after the last ?> used to close the php code, there were three blank lines that, when deleted, did everything back to normal.
I think it maybe can help someone.