this normally happens with filezilla. we had a post from 2010 about this here.
so this is an update, first check if you using the correct login info, then if still not working do:
- Open Filezilla and open the settings (under the Edit menu)
- Under “Connection” select “FTP”
- The section at the top is called Transfer Mode. Within that, choose “Passive Mode”
- Click OK. You should now be able to connect.
With ftp and continuous use, you can obtain stable results within 3 minutes without the hassles of going into customer support. using the filezilla for me is the best, perhaps whitelist first your IP on the server firewall.
I think this is some issue related to the csf firewall, I had it last month on a cpanel hosting, as soon as I disabled csf it worked.
as Chris says it is because of the firewall, try to reset it or restart the csf.