SOCKS4 proxy server sometimes rejects FTP data connection?

The FTP Extended Passive Mode (EPSV) continues to be both a solution to problems AND the cause of problems. The Chilkat FTP2 component will automatically use EPSV (as opposed to PASV) if it detects the FTP server supports EPSV. This is generally a good thing to do, and often solves problems. However, occasionally it can be the cause of problems. This is the case here:

A Chilkat customer’s SOCKS4 proxy server sometimes rejects the FTP data connection when EPSV mode is used. The solution is to set the UseEpsv property = False after connecting to the FTP server.

In general, if passive mode seems to work with FTP clients such as FileZilla, but not Chilkat, it is possible that EPSV is the culprit. Try forcibly turning EPSV off by setting the UseEpsv property = False. Then check to see if the problem is resolved.