I received this error because I rebooted the server with the FTP-directory (target), so the SQL-Server (source) could not access to this directory for a while.
I got this error due to a setup mistake. I setup a new FTP site in IIS 6 using the "Isolate Users" option. I then created folders in ftproot for each user getting access. What I did not realize is that IIS 6 expects a folder indicating the source of the account. Here is what I mean:
I was missing the middle folder in my structure.
In my case, the problem was resolved by restarting the FTP service.
May also occur when your IP address is not listed in the "TCP/IP access restrictions" on the "Directory security" tab, when the option "By default, all computers will be: denied access" has been selected.
As per Microsoft: "This problem occurs when the home directory of the FTP site does not exist or the user does not have Read permissions to the home directory". See ME221934
for more details.
This event occurs when IIS FTP component allows anonymous access but the IUSR_computer_name account does not have rights to the directory configured as the FTP root.
I had this problem when the read (and write if required) check boxes were not ticked in the FTP site directory section of the Home Directory tab (of the Default Web Site Properties dialogue box within IIS - NT4).