Wrong password gives FTP error

-- url of the page with the problem -- : northernnevadagold.com
-- HikaShop version -- : latest one
-- Joomla version -- : Joomla! 3.6.4 Stable [ Noether ] 21-October-2016 16:33 GMT
-- PHP version -- : 5.5.9-1ubuntu4.20
-- Browser(s) name and version -- : All
-- Error-message(debug-mod must be tuned on) -- : 35 JFTP: :append: Bad response

When the user enters an incorrect password, the site throws:

35 JFTP: :append: Bad response

Is there some file or directory that the webserver user must write?

Thanks

Oh, of course. Hikashop checkout is just using Joomla login. My apologies!