SFTP doesn't work (Error:Please check login credentials again)

I cannot connect to server using SFTP with Error:Please check login credentials again.
In log file the following error is raised:
[2019/09/13 16:39:51.085] [MESSAGE ] [ 7112] [NETWORK ] [INFORMATION] Using SSH private key file ‘C:/Users/…/…/private_key.ppk’
[2019/09/13 16:39:51.086] [MESSAGE ] [ 7112] [NETWORK ] [INFORMATION] SSH public key authentication failed: Unable to extract public key from private key file: Wrong passphrase or invalid/unrecognized private key file format
[2019/09/13 16:39:51.086] [MESSAGE ] [ 7112] [NETWORK ] [INFORMATION] Authentication failure
[2019/09/13 16:39:51.086] [MESSAGE ] [ 7112] [NETWORK ] [INFORMATION] Closing connection 0


Thank you for using NetDrive.

I think you are using putty format private key.

Unfortunately, NetDrive supports openssh format private key file.

If you convert your private key to openssh format, you can connect.


thanks a lot