I like to do simple sanity checks on the setup to make sure the network is routing the connection properly. If the PLC is behind a device such as a (VPN) router, I like to plug in a laptop as well to to make sure you can use simple command prompt FTP commands to ensure it's able to connect to the windows PC with FTP server. Ensures all the external settings are sufficient for the BRX to be able to do the same.
Also, I'm not 100% sure, but you may need to close the SD card's file (with FILECLOSE instruction) before being able to FTPPUT it?