Can't create directory - SSH_FXP_REALPATH with SFTP version 6 a problem in 5.7.6

I recently upgraded to 5.7.6 and found that I couldn't create directories using SFTP.

After some reading and investigation I found that this was a problem that was fixed in 5.7.1. (http://bugs.proftpd.org/show_bug.cgi?id=4160).

Rolling back to 5.7.1 fixed the problem.

Another workaround was to change to version 5.

So...still a problem in latest release.

Please attach a full log file showing the problem (using the latest version of WinSCP).

I've attached the log file.
I performed one directory creation using the Normal level of logging and one using Debug 1.

Thanks for the log.

The initial workaround implemented in 5.7.1 was not conforming to SFTP specification. So it broke compatibility with some other servers.
I had to make the workaround apply for ProFTPD specifically only, since 5.7.2.
See https://winscp.net/tracker/1308

But your server does not identify itself as ProFTPD, but as "netfirms FTP Server Ready". So WinSCP does not apply the workaround.

You should contact your hosting provider to upgrade their ProFTPD server. Or at least re-configure it to correctly identify as ProFTPD.