425 Unable to build data connection: Connection timed out

This error can happen when trying to transfer a file or list a directory in Active (PORT) mode. The problem is usually solved by switching to Passive mode. Set the Ftp2.Passive property equal to True.

Explanation of the problem: In Active mode, the data connection is setup like this: The client sends a PORT command telling the server the port where it will be listening for the data connection. The server receives the PORT command and initiates a connection to the client’s IP/port. However, if a firewall is blocking the incoming connection, then it will go unanswered, and the server will timeout waiting for the connection to be accepted.