We do usually see this 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. Synchronize FTP passwords using Main >> cPanel >> Synchronize FTP Passwords option in whm.
2. Restart FTP server using Main >> Restart Services >> FTP Server (ProFTPd/PureFTPd) option.
2. /etc/init.d/pure-ftp restart
This will fix the issue.