This issue has been discussed about a lot on the forum, I wasn't able to replicate the error, until I did modified the FTP path. The solution to this error turns out to be simple.

Enter the FULL ftp path WITH a leading slash. So when you log in with FTP on your server and you will have to enter the directory www for your web root, enter the FTP path: "/www". If you have to browse into a directory public_html for you Joomla! files, enter the ftp path: "/public_html"

So all with a leading slash. 

Correct:

/www
/public_html
/domains/demo.joomla-addons.org/www

Wrong:

www
public_html
domains/demo.joomla-addons.org/www

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