@Ed: Please post a log with "Optimize connection buffer size" turned off.

Could it be that there are too many files to load on the server directory you are trying to connect to? The buffer settings seemed to work for me for about a month, then it stopped working with the same message.

@samr: Duplicate post:
https://winscp.net/forum/viewtopic.php?t=15777

For some reason, the site I connect to doesn't work well with the "Optimize connection buffer size" enabled, and whenever I had that on while downloading files larger than a few megabytes, I'd get this error: Server unexpectedly closed network connection.

Fortunately, I found how to turn it off and (in the GUI version at least) all my transfers are successful. On the contrary, in batch mode from a script file, even after setting -rawsettings SendBuf=0 appended to the open command, the connection will "unexpectedly close" on files larger than a few megabytes.

Does SendBuf=0 completely turn off the feature as the GUI checkbox does?

Thank you.

The -rawsettings is not a command, but a switch to open command:
https://winscp.net/eng/docs/scriptcommand_open

I've added an example:
https://winscp.net/eng/docs/rawsettings#example

I've been trying to get this to work in a SSIS 2005 Execute Process Task but keep getting the message "Unknown command -rawsettings"

I'm using it as the first line of my script like so: -rawsettings SendBuf=0

Is there a different way I should be using this?

Thanks, Keith

Awesome. Thanks.

See https://winscp.net/eng/docs/rawsettings

Is there a way to do this in the script? I tried using "option optimize connection buffer size off" but this is throwing an error.

Thanks.