The remote server returned an error: 227 Entering Passive Mode (500 oops vs_utility_recv_peek: no data)

Question

I am having a problem connecting a Windows service to an FTP site.

I inherited a Windows service from another developer. The service connects to a 3rd party server,

Answer 1

The issue is now resolved. It turned out to be Kaspersky's built-in firewall that was blocking the connection. It's annoying that it didn't present me with a warning when I tried to connect, but reassuring to know my PC is safe.

The clue was in the detail of the 227 return:

10051 – A socket operation was attempted to an unreachable network

Also, for anyone reaching this via Google etc, the remote server was configured to only allow Passive connections, which is why I was getting the 500 syntax error. Studying a Wire capture when downloading a file revealed that Filezilla actually reverts to Passive mode automatically if Active is selected but fails.

The code in my original post works fine now.