Thanks for your report.
I have sent you an email to address you have used to register on this forum.
Also i ve just tested .net native FtpWebRequest class and it connects to FTP server while winscp does not.
I have a .net 2.0 application witch uses winscp assembly to transfer files to ftp. My application runs on about 400 client machines. And sometimes on one of them winscp becomes unable to connect to any FTP server. Others work fine.
My app is started by windows service which runs at normal user (not system user). And if i login as that user and run my app manually it connects! to server. So the user is the same. But manually it works and if runned by windows service does not. I can restart as many times as i can. My application totally closes before next try to connect.
It looks like after reboot it works again. But i'm not sure 100% if reboot makes it work again.
It may happen on one machine of 400 in a day or two. So it's hard to reproduce but happens regularly.
I m using winscp 5.1.2 but tried 5.1.5 on problematic machine and it didn't work either.
Problem happens on windows 7 (Others not tested).
I attached debug log to this message(i replaced ftp credentials)
May this problem happen because sometimes my app opens two simultaneous connections to the same server?
If you need any additional information please contact me.