FileZIlla - Fix SFTP Protocol Error - Too Many Authentication Failures

The Problem

I had just set up a fresh user account on my Ubuntu server for a client, and was testing the connection in FileZilla (using SFTP) when I was getting the following error.

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Status: Connecting to XXX.XXX.XXX.XXX...
Response:   fzSftp started, protocol_version=9
Command:    open "myUsername@XXX.XXX.XXX.XXX" 22
Error:  FATAL ERROR: Remote side sent disconnect message
Error:  type 2 (protocol error):
Error:  "Too many authentication failures"
Error:  Could not connect to server

The Solution

It turns out that even though I had set FileZilla to use a password, it was trying the keys inside my $HOME/.ssh directory. After it had tried and failed with enough of these, it bails out with "too many authentication failures". One Stack Overflow post suggested keeping no more than 4 keys in there. However, I found the easier solution was to just set the SSH_AUTH_SOCK to null before running filezilla, like so:

SSH_AUTH_SOCK=null filezilla &

As this forum post explains:

This sets the SSH_AUTH_SOCK shell environment variable only for this instance of filezilla, which means any other program (e.g. ssh) can still use the agent while filezilla wont be able to do so.