I was getting authentication failed error in my webserver which runs on ISPCONFIG 3.I tried changing password many times from Ispconfig web console. But didn’t worked for me. I tried from ftp client (filezilla) and from my gnome-terminal too. While trying to connect error returned by server is 
User bikram OK. Password required
PASS (hidden)
530 Login authentication failed
From googling I fixed the above error. The solution that worked for me is:
/etc/pure-ftpd/db/mysql.conf
I’ve changed the line
MySQLServer 127.0.0.1
to
MySQLServer localhost
Restart pure-ftpd
Few weeks ago I faced Problem problem in establishing connection in ftp. Go through my older post of puref-ftpd here.
