I have used a number of different firewalls in the past, but settled on Comodo some time ago as it seemed to be rather good.
Now, I have disabled it.
Without changing any other settings what-so-ever, I cannot ftp files using Filezilla, SmartFTP, FTPCommander and others without experiencing major problems.
The files I upload appear on the server with ZERO BYTE size!
I switched off the Comodo firewall and everything worked perfectly again.
My empirical evidence is that this is a Comodo Firewall issue.
Does anybody know how to get around this?
I am happy to continue testing, but for the time-being, Comodo Firewall is switched off because it is a greater liability than a help.