Server refused our key

I try use winscp from command line:

C:\Program Files (x86)\WinSCP>WinSCP.com scp://username@xxx.yyyy.net /privatekey=xxxxxxxx-pri.ppk
or
C:\Program Files (x86)\WinSCP>WinSCP.com sftp://username@xxx.yyyy.net /privatekey=xxxxxxxx-pri.ppk

but result is:

Searching for host...
Connecting to host...
Authenticating...
Using username "username".
Server refused our key.
Password:

i have private key in winscp folder.

I try it (.ppk, username, server, scp/sftp) in GUI and it works...strange.
I use WinSP Version 4.2.1. (Build 428)

Key that i have is not privatekey but hostkey in winscp...

In command line:

winscp.com /hostkey=xxxxxxxx-pri.ppk ....