This is a very common error while accessing ftp even though you entered the correct login details. This is because ftp passwords and cpanel passwords are stored in separate locations and sometimes the ftp passwords wont get updated when you update cpanel passwords. To resolve this issue do the following steps.
1. Switch FTP from Pure-ftpd to Proftpd in WHM > FTP Configuration switch it back to again.
2. Synchronize FTP passwords using Main >> cPanel >> Synchronize FTP Passwords option in whm.
3. Make sure that the local machine IP address isn’t blocked in server firewall.
4. Restart FTP server using Main >> Restart Services >> FTP Server (ProFTPd/PureFTPd) option.
Or from shell
2. /etc/init.d/pure-ftp restart