There's not much more I can suggest you that what they already suggested you at your duplicate post at FileZilla forum:
IP Block? Error: Failed to retrieve directory listing - FileZilla Forums

No one an idea? :(

Thank you very much for your Answer.
I removed the tick in the checkbox at "Passive Mode" before, because i got other Errors with that:

Timeout detected. (data connection)
Could not retrieve directory listing
Error listing directory '/'.

Sorry, i forgot about that.
The attached log is on level 2 - Debug and in Passive mode.

It looks like you are using the FTP active mode. Why? Did you try the default passive mode? In any case, post a session log file.

Hello,
I have a weird problem.
When trying to connect to an FTP server of a client in Hungary, I get following error message:

Could not retrieve directory listing
I won't open a connection to 192.168.178.120 (only to XX.XXX.XX.XX)

The first IP is my internal IP of my PC in my network.
The second IP is my external IPv4-IP.

The protocol of the FTP server FTP & explicit FTPS over port 21.

Is there an IP or country filter at the FTP server or is it a setting on my site?
I tried it with FileZilla too, there I also can't connect, so it seems not to be a WinSCP-problem in general.

Thank you very much in advance,
Christian Hange